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LM628 LM629 Precision Motion Controller
February 1995
LM628 LM629 Precision Motion Controller
General Description
The LM628 LM629 are dedicated motion-control processors designed for use with a variety of DC and brushless DC servo motors and other servomechanisms which provide a quadrature incremental position feedback signal The parts perform the intensive real-time computational tasks required for high performance digital motion control The host control software interface is facilitated by a high-level command set The LM628 has an 8-bit output which can drive either an 8-bit or a 12-bit DAC The components required to build a servo system are reduced to the DC motor actuator an incremental encoder a DAC a power amplifier and the LM628 An LM629-based system is similar except that it provides an 8-bit PWM output for directly driving H-switches The parts are fabricated in NMOS and packaged in a 28-pin dual in-line package or a 24-pin surface mount package (LM629 only) Both 6 MHz and 8 MHz maximum frequency versions are available with the suffixes -6 and -8 respectively used to designate the versions They incorporate an SDA core processor and cells designed by SDA
Features
Y Y Y Y Y Y Y
Y Y Y Y
Y
32-bit position velocity and acceleration registers Programmable digital PID filter with 16-bit coefficients Programmable derivative sampling interval 8- or 12-bit DAC output data (LM628) 8-bit sign-magnitude PWM output data (LM629) Internal trapezoidal velocity profile generator Velocity target position and filter parameters may be changed during motion Position and velocity modes of operation Real-time programmable host interrupts 8-bit parallel asynchronous host interface Quadrature incremental encoder interface with index pulse input Available in a 28-pin dual in-line package or a 24-pin surface mount package (LM629 only)
TRI-STATE is a registered trademark of National Semiconductor Corporation
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FIGURE 1 Typical System Block Diagram
Connection Diagrams
LM628N LM629N LM629M
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Do not connect
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Order Number LM629M-6 LM629M-8 LM628N-6 LM628N-8 LM629N-6 or LM629N-8 See NS Package Number M24B or N28B
C1995 National Semiconductor Corporation TL H 9219 RRD-B30M115 Printed in U S A
Absolute Maximum Ratings (Note 1)
If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Voltage at Any Pin with Respect to GND Ambient Storage Temperature Lead Temperature 28-pin Dual In-Line Package (Soldering 4 sec ) 24-pin Surface Mount Package (Soldering 10 sec )
b 0 3V to a 7 0V b 65 C to a 150 C
Operating Ratings
Temperature Range Clock Frequency LM628N-6 LM629N-6 LM629M-6 LM628N-8 LM629N-8 LM629M-8 VDD Range
b 40 C k TA k a 85 C
1 0 MHz k fCLK k 6 0 MHz 1 0 MHz k fCLK k 8 0 MHz 4 5V k VDD k 5 5V
260 C 300 C 605 mW 2000V fCLK e 6 MHz) Tested Limits Min Max 110 mA Units
Maximum Power Dissipation (TA s 85 C Note 2) ESD Tolerance (CZAP e 120 pF RZAP e 1 5k)
DC Electrical Characteristics (VDD and TA per Operating Ratings
Symbol IDD INPUT VOLTAGES VIH VIL IIN Logic 1 Input Voltage Logic 0 Input Voltage Input Currents 0 s VIN s VDD Parameter Supply Current Conditions Outputs Open
20 08
b 10
V V mA
10
OUTPUT VOLTAGES VOH VOL IOUT Logic 1 Logic 0 TRI-STATE Output Leakage Current IOH e b1 6 mA IOL e 1 6 mA 0 s VOUT s VDD
b 10
24 04 10
V V mA
AC Electrical Characteristics
(VDD and TA per Operating Ratings fCLK e 6 MHz CLOAD e 50 pF Input Test Signal tr e tf e 10 ns) Timing Interval ENCODER AND INDEX TIMING (See Figure 2 ) Motor-Phase Pulse Width Dwell-Time per State Index Pulse Setup and Hold (Relative to A and B Low) CLOCK AND RESET TIMING (See Figure 3 ) Clock Pulse Width LM628N-6 LM629N-6 LM629M-6 LM628N-8 LM629N-8 LM629M-8 Clock Period LM628N-6 LM629N-6 LM629M-6 LM628N-8 LM629N-8 LM629M-8 Reset Pulse Width T4 T4 T5 T5 T6 78 57 166 125 8 fCLK ns ns ns ns ms T1 T2 16 fCLK 8 fCLK 0 ms ms ms T Min Tested Limits Max Units
T3
2
AC Electrical Characteristics (Continued) (VDD and TA per Operating Ratings fCLK e 6 MHz CLOAD e 50 pF Input Test Signal tr e tf e 10 ns)
Timing Interval STATUS BYTE READ TIMING (See Figure 4 ) Chip-Select Setup Hold Time Port-Select Setup Time Port-Select Hold Time Read Data Access Time Read Data Hold Time RD High to Hi-Z Time COMMAND BYTE WRITE TIMING (See Figure 5 ) Chip-Select Setup Hold Time Port-Select Setup Time Port-Select Hold Time Busy Bit Delay WR Pulse Width Write Data Setup Time Write Data Hold Time DATA WORD READ TIMING (See Figure 6 ) Chip-Select Setup Hold Time Port-Select Setup Time Port-Select Hold Time Read Data Access Time Read Data Hold Time RD High to Hi-Z Time Busy Bit Delay Read Recovery Time DATA WORD WRITE TIMING (See Figure 7 ) Chip-Select Setup Hold Time Port-Select Setup Time Port-Select Hold Time Busy Bit Delay WR Pulse Width Write Data Setup Time Write Data Hold Time Write Recovery Time T7 T8 T9 T13 T14 T15 T16 T18 100 50 120 120 0 30 30 (Note 3) ns ns ns ns ns ns ns ns T7 T8 T9 T10 T11 T12 T13 T17 120 0 180 (Note 3) 0 30 30 180 ns ns ns ns ns ns ns ns T7 T8 T9 T13 T14 T15 T16 100 50 120 0 30 30 (Note 3) ns ns ns ns ns ns ns T7 T8 T9 T10 T11 T12 0 180 0 30 30 180 ns ns ns ns ns ns T Min Tested Limits Max Units
Note 1 Absolute Maximum Ratings indicate limits beyond which damage to the device may occur DC and AC electrical specifications do not apply when operating the device beyond the above Operating Ratings Note 2 When operating at ambient temperatures above 70 C the device must be protected against excessive junction temperatures Mounting the package on a printed circuit board having an area greater than three square inches and surrounding the leads and body with wide copper traces and large uninterrupted areas of copper such as a ground plane suffices The 28-pin DIP (N) and the 24-pin surface mount package (M) are molded plastic packages with solid copper lead frames Most of the heat generated at the die flows from the die through the copper lead frame and into copper traces on the printed circuit board The copper traces act as a heat sink Double-sided or multi-layer boards provide heat transfer characteristics superior to those of single-sided boards Note 3 In order to read the busy bit the status byte must first be read The time required to read the busy bit far exceeds the time the chip requires to set the busy bit It is therefore impossible to test actual busy bit delay The busy bit is guaranteed to be valid as soon as the user is able to read it
3
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FIGURE 2 Quadrature Encoder Input Timing
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FIGURE 3 Clock and Reset Timing
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FIGURE 4 Status Byte Read Timing
4
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FIGURE 5 Command Byte Write Timing
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FIGURE 6 Data Word Read Timing
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FIGURE 7 Data Word Write Timing 5
Pinout Description
(See Connection Diagrams) Pin numbers for the 24-pin surface mount package are indicated in parentheses Pin 1 (17) Index (IN) Input Receives optional index pulse from the encoder Must be tied high if not used The index position is read when Pins 1 2 and 3 are low Pins 2 and 3 (18 and 19) Encoder Signal (A B) Inputs Receive the two-phase quadrature signals provided by the incremental encoder When the motor is rotating in the positive (``forward'') direction the signal at Pin 2 leads the signal at Pin 3 by 90 degrees Note that the signals at Pins 2 and 3 must remain at each encoder state (See Figure 9 ) for a minimum of 8 clock periods in order to be recognized Because of a four-to-one resolution advantage gained by the method of decoding the quadrature encoder signals this corresponds to a maximum encoder-state capture rate of 1 0 MHz (fCLK e 8 0 MHz) or 750 kHz (fCLK e 6 0 MHz) For other clock frequencies the encoder signals must also remain at each state a minimum of 8 clock periods Pins 4 to 11 (20 to 24 and 2 to 4) Host I O Port (D0 to D7) Bi-directional data port which connects to host computer processor Used for writing commands and data to the LM628 and for reading the status byte and data from the LM628 as controlled by CS (Pin 12) PS (Pin 16) RD (Pin 13) and WR (Pin 15) Pin 12 (5) Chip Select (CS) Input Used to select the LM628 for writing and reading operations Pin 13 (6) Read (RD) Input Used to read status and data Pin 14 (7) Ground (GND) Power-supply return pin Pin 15 (8) Write (WR) Input Used to write commands and data Pin 16 (9) Port Select (PS) Input Used to select command or data port Selects command port when low data port when high The following modes are controlled by Pin 16 1 Commands are written to the command port (Pin 16 low) 2 Status byte is read from command port (Pin 16 low) and 3 Data is written and read via the data port (Pin 16 high) Pin 17 (10) Host Interrupt (HI) Output This active-high signal alerts the host (via a host interrupt service routine) that an interrupt condition has occurred Pins 18 to 25 DAC Port (DAC0 to DAC7) Output port which is used in three different modes 1 LM628 (8-bit output mode) Outputs latched data to the DAC The MSB is Pin 18 and the LSB is Pin 25 2 LM628 (12-bit output mode) Outputs two multiplexed 6-bit words The less-significant word is output first The MSB is on Pin 18 and the LSB is on Pin 23 Pin 24 is used to demultiplex the words Pin 24 is low for the less-significant word The positive-going edge of the signal on Pin 25 is used to strobe the output data Figure 8 shows the timing of the multiplexed signals 3 LM629 (sign magnitude outputs) Outputs a PWM sign signal on Pin 18 (11 for surface mount) and a PWM magnitude signal on Pin 19 (13 for surface mount) Pins 20 to 25 are not used in the LM629 Figure 11 shows the PWM output signal format Pin 26 (14) Clock (CLK) Input Receives system clock Pin 27 (15) Reset (RST) Input Active-low positive-edge triggered resets the LM628 to the internal conditions shown below Note that the reset pulse must be logic low for a minimum of 8 clock periods Reset does the following 1 Filter coefficient and trajectory parameters are zeroed 2 Sets position error threshold to maximum value (7FFF hex) and effectively executes command LPEI 3 The SBPA SBPR interrupt is masked (disabled) 4 The five other interrupts are unmasked (enabled) 5 Initializes current position to zero or ``home'' position 6 Sets derivative sampling interval to 2048 fCLK or 256 ms for an 8 0 MHz clock 7 DAC port outputs 800 hex to ``zero'' a 12-bit DAC and then reverts to 80 hex to ``zero'' an 8-bit DAC Immediately after releasing the reset pin from the LM628 the status port should read `00' If the reset is successfully completed the status word will change to hex `84' or `C4' within 1 5 ms If the status word has not changed from hex `00' to `84' or `C4' within 1 5 ms perform another reset and repeat the above steps To be certain that the reset was properly performed execute a RSTI command If the chip has reset properly the status byte will change from hex `84' or `C4' to hex `80' or `C0' If this does not occur perform another reset and repeat the above steps Pin 28 (16) Supply Voltage (VDD) Power supply voltage ( a 5V)
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FIGURE 8 12-Bit Multiplexed Output Timing
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Theory of Operation
INTRODUCTION The typical system block diagram (See Figure 1 ) illustrates a servo system built using the LM628 The host processor communicates with the LM628 through an I O port to facilitate programming a trapezoidal velocity profile and a digital compensation filter The DAC output interfaces to an external digital-to-analog converter to produce the signal that is power amplified and applied to the motor An incremental encoder provides feedback for closing the position servo loop The trapezoidal velocity profile generator calculates the required trajectory for either position or velocity mode of operation In operation the LM628 subtracts the actual position (feedback position) from the desired position (profile generator position) and the resulting position error is processed by the digital filter to drive the motor to the desired position Table I provides a brief summary of specifications offered by the LM628 LM629 POSITION FEEDBACK INTERFACE The LM628 interfaces to a motor via an incremental encoder Three inputs are provided two quadrature signal inputs and an index pulse input The quadrature signals are used to keep track of the absolute position of the motor Each time a logic transition occurs at one of the quadrature inputs the LM628 internal position register is incremented or decremented accordingly This provides four times the resolution over the number of lines provided by the encoder See Figure 9 Each of the encoder signal inputs is synchronized with the LM628 clock The optional index pulse output provided by some encoders assumes the logic-low state once per revolution If the LM628 is so programmed by the user it will record the absolute motor position in a dedicated register (the index register) at the time when all three encoder inputs are logic low If the encoder does not provide an index output the LM628 index input can also be used to record the home position of the motor In this case typically the motor will close a switch which is arranged to cause a logic-low level at the index input and the LM628 will record motor position in the index register and alert (interrupt) the host processor Permanently grounding the index input will cause the LM628 to malfunction
TABLE I System Specifications Summary Position Range Velocity Range Acceleration Range Motor Drive Output Operating Modes Feedback Device Control Algorithm Sample Intervals
b 1 073 741 824 to 1 073 741 823 counts
0 to 1 073 741 823 216 counts sample ie 0 to 16 383 counts sample with a resolution of 1 216 counts sample 0 to 1 073 741 823 216 counts sample sample ie 0 to 16 383 counts sample sample with a resolution of 1 216 counts sample sample LM628 8-bit parallel output to DAC or 12-bit multiplexed output to DAC LM629 8-bit PWM sign magnitude signals Position and Velocity Incremental Encoder (quadrature signals support for index pulse) Proportional Integral Derivative (PID) (plus programmable integration limit) Derivative Term Programmable from 2048 fCLK to (2048 256) fCLK in steps of 2048 fCLK (256 to 65 536 ms for an 8 0 MHz clock) Proportional and Integral 2048 fCLK
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Theory of Operation (Continued)
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FIGURE 9 Quadrature Encoder Signals
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FIGURE 10 Typical Velocity Profiles VELOCITY PROFILE (TRAJECTORY) GENERATION The trapezoidal velocity profile generator computes the desired position of the motor versus time In the position mode of operation the host processor specifies acceleration maximum velocity and final position The LM628 uses this information to affect the move by accelerating as specified until the maximum velocity is reached or until deceleration must begin to stop at the specified final position The deceleration rate is equal to the acceleration rate At any time during the move the maximum velocity and or the target position may be changed and the motor will accelerate or decelerate accordingly Figure 10 illustrates two typical trapezoidal velocity profiles Figure 10 (a) shows a simple trapezoid while Figure 10 (b) is an example of what the trajectory looks like when velocity and position are changed at different times during the move When operating in the velocity mode the motor accelerates to the specified velocity at the specified acceleration rate and maintains the specified velocity until commanded to stop The velocity is maintained by advancing the desired position at a constant rate If there are disturbances to the motion during velocity mode operation the long-time average velocity remains constant If the motor is unable to maintain the specified velocity (which could be caused by a locked rotor for example) the desired position will continue to be increased resulting in a very large position error If this 8 condition goes undetected and the impeding force on the motor is subsequently released the motor could reach a very high velocity in order to catch up to the desired position (which is still advancing as specified) This condition is easily detected see commands LPEI and LPES All trajectory parameters are 32-bit values Position is a signed quantity Acceleration and velocity are specified as 16-bit positive-only integers having 16-bit fractions The integer portion of velocity specifies how many counts per sampling interval the motor will traverse The fractional portion designates an additional fractional count per sampling interval Although the position resolution of the LM628 is limited to integer counts the fractional counts provide increased average velocity resolution Acceleration is treated in the same manner Each sampling interval the commanded acceleration value is added to the current desired velocity to generate a new desired velocity (unless the command velocity has been reached) One determines the trajectory parameters for a desired move as follows If for example one has a 500-line shaft encoder desires that the motor accelerate at one revolution per second per second until it is moving at 600 rpm and then decelerate to a stop at a position exactly 100 revolutions from the start one would calculate the trajectory parameters as follows
Theory of Operation (Continued)
let let P e target position (units e encoder counts) R e encoder lines 4 (system resolution) 4 e 2000 a constant torque loading the motor will still be able to achieve zero position error The third term the derivative term provides a force proportional to the rate of change of position error It acts just like viscous damping in a damped spring and mass system (like a shock absorber in an automobile) The sampling interval associated with the derivative term is user-selectable this capability enables the LM628 to control a wider range of inertial loads (system mechanical time constants) by providing a better approximation of the continuous derivative In general longer sampling intervals are useful for low-velocity operations In operation the filter algorithm receives a 16-bit error signal from the loop summing-junction The error signal is saturated at 16 bits to ensure predictable behavior In addition to being multiplied by filter coefficient kp the error signal is added to an accumulation of previous errors (to form the integral signal) and at a rate determined by the chosen derivative sampling interval the previous error is subtracted from it (to form the derivative signal) All filter multiplications are 16-bit operations only the bottom 16 bits of the product are used The integral signal is maintained to 24 bits but only the top 16 bits are used This scaling technique results in a more usable (less sensitive) range of coefficient ki values The 16 bits are right-shifted eight positions and multiplied by filter coefficient ki to form the term which contributes to the motor control output The absolute magnitude of this product is compared to coefficient il and the lesser appropriately signed magnitude then contributes to the motor control signal The derivative signal is multiplied by coefficient kd each derivative sampling interval This product contributes to the motor control output every sample interval independent of the user-chosen derivative sampling interval The kp limited ki and kd product terms are summed to form a 16-bit quantity Depending on the output mode (wordsize) either the top 8 or top 12 bits become the motor control output signal LM628 READING AND WRITING OPERATIONS The host processor writes commands to the LM628 via the host I O port when Port Select (PS) input (Pin 16) is logic low The desired command code is applied to the parallel port line and the Write (WR) input (Pin 15) is strobed The command byte is latched into the LM628 on the rising edge of the WR input When writing command bytes it is necessary to first read the status byte and check the state of a flag called the ``busy bit'' (Bit 0) If the busy bit is logic high no command write may take place The busy bit is never high longer than 100 ms and typically falls within 15 ms to 25 ms The host processor reads the LM628 status byte in a similar manner by strobing the Read (RD) input (Pin 13) when PS (Pin 16) is low status information remains valid as long as RD is low Writing and reading data to from the LM628 (as opposed to writing commands and reading status) are done with PS (Pin 16) logic high These writes and reads are always an integral number (from one to seven) of two-byte words with the first byte of each word being the more significant Each byte requires a write (WR) or read (RD) strobe When transferring data words (byte-pairs) it is necessary to first read the status byte and check the state of the busy bit When the 9 then R e 500
and P e 2000 desired number of revolutions P e 2000 100 revs e 200 000 counts (value to load) P (coding) e 00030D40 (hex code written to LM628) let let let V e velocity (units e counts sample) T e sample time (seconds) e 341 ms (with 6 MHz clock) C e conversion factor e 1 minute 60 seconds
and V V V V V let
then V e R T C desired rpm e 2000 341E b 6 1 60 600 rpm e 6 82 counts sample (scaled) e 6 82 65 536 e 446 955 52 (rounded) e 446 956 (value to load) (coding) e 0006D1EC (hex code written to LM628)
A e acceleration (units e counts sample sample) A e R T T desired acceleration (rev sec sec) then A e 2000 341Eb6 341E-6 1 rev sec sec and A e 2 33Eb4 counts sample sample A (scaled) e 2 33Eb4 65 536 e 15 24 A (rounded) e 15 (value to load) A (coding) e 0000000F (hex code written to LM628) The above position velocity and acceleration values must be converted to binary codes to be loaded into the LM628 The values shown for velocity and acceleration must be multiplied by 65 536 (as shown) to adjust for the required integer fraction format of the input data Note that after scaling the velocity and acceleration values literal fractional data cannot be loaded the data must be rounded and converted to binary The factor of four increase in system resolution is due to the method used to decode the quadrature encoder signals see Figure 9 PID COMPENSATION FILTER The LM628 uses a digital Proportional Integral Derivative (PID) filter to compensate the control loop The motor is held at the desired position by applying a restoring force to the motor that is proportional to the position error plus the integral of the error plus the derivative of the error The following discrete-time equation illustrates the control performed by the LM628
n
u(n) e kp e(n) a ki
Ne0
e(n) a
kd e(n ) b e(n b 1) (Eq 1) where u(n) is the motor control signal output at sample time n e(n) is the position error at sample time n n indicates sampling at the derivative sampling rate and kp ki and kd are the discrete-time filter parameters loaded by the users The first term the proportional term provides a restoring force porportional to the position error just as does a spring obeying Hooke's law The second term the integration term provides a restoring force that grows with time and thus ensures that the static position error is zero If there is
Theory of Operation (Continued)
busy bit is logic low the user may then sequentially transfer both bytes comprising a data word but the busy bit must again be checked and found to be low before attempting to transfer the next byte pair (when transferring multiple words) Data transfers are accomplished via LM628-internal interrupts (which are not nested) the busy bit informs the host processor when the LM628 may not be interrupted for data transfer (or a command byte) If a command is written when the busy bit is high the command will be ignored The busy bit goes high immediately after writing a command byte or reading or writing a second byte of data (See Figures 5 thru 7 ) MOTOR OUTPUTS The LM628 DAC output port can be configured to provide either a latched eight-bit parallel output or a multiplexed 12-bit output The 8-bit output can be directly connected to a flow-through (non-input-latching) D A converter the 12-bit output can be easily demultiplexed using an external 6-bit latch and an input-latching 12-bit D A converter The DAC output data is offset-binary coded the 8-bit code for zero is 80 hex and the 12-bit code for zero is 800 hex Values less than these cause a negative torque to be applied to the motor and conversely larger values cause positive motor torque The LM628 when configured for 12-bit output provides signals which control the demultiplexing process See Figure 8 for details The LM629 provides 8-bit sign and magnitude PWM output signals for directly driving switch-mode motor-drive amplifiers Figure 11 shows the format of the PWM magnitude output signal
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Note Sign output (pin 18) not shown
FIGURE 11 PWM Output Signal Format
TABLE II LM628 User Command Set Command RESET PORT8 PORT12 DFH SIP LPEI LPES SBPA SBPR MSKI RSTI LFIL UDF LTRJ STT RDSTAT RDSIGS RDIP RDDP RDRP RDDV RDRV RDSUM Type Initialize Initialize Initialize Initialize Interrupt Interrupt Interrupt Interrupt Interrupt Interrupt Interrupt Filter Filter Trajectory Trajectory Report Report Report Report Report Report Report Report Description Reset LM628 Select 8-Bit Output Select 12-Bit Output Define Home Set Index Position Interrupt on Error Stop on Error Set Breakpoint Absolute Set Breakpoint Relative Mask Interrupts Reset Interrupts Load Filter Parameters Update Filter Load Trajectory Start Motion Read Status Byte Read Signals Register Read Index Position Read Desired Position Read Real Position Read Desired Velocity Read Real Velocity Read Integration Sum Hex 00 05 06 02 03 1B 1A 20 21 1C 1D 1E 04 1F 01 None 0C 09 08 0A 07 0B 0D Data Bytes 0 0 0 0 0 2 2 4 4 2 2 2 to 10 0 2 to 14 0 1 2 4 4 4 4 2 2 Note 1 2 2 1 1 1 1 1 1 1 1 1 1 1 3 14 1 1 1 1 1 1 1
Note 1 Commands may be executed ``On the Fly'' during motion Note 2 Commands not applicable to execution during motion Note 3 Command may be executed during motion if acceleration parameter was not changed Note 4 Command needs no code because the command port status-byte read is totally supported by hardware
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User Command Set
GENERAL The following paragraphs describe the user command set of the LM628 Some of the commands can be issued alone and some require a supporting data structure As examples the command STT (STarT motion) does not require additional data command LFIL (Load FILter parameters) requires additional data (derivative-term sampling interval and or filter parameters) Commands are categorized by function initialization interrupt control filter control trajectory control and data reporting The commands are listed in Table II and described in the following paragraphs Along with each command name is its command-byte code the number of accompanying data bytes that are to be written (or read) and a comment as to whether the command is executable during motion
mediately executed This command must not be issued when using an 8-bit converter or the LM629 the PWM-output version of the LM628 DFH COMMAND DeFine Home Command Code 02 Hex Data Bytes None Executable During Motion Yes This command declares the current position as ``home'' or absolute position 0 (Zero) If DFH is executed during motion it will not affect the stopping position of the on-going move unless command STT is also executed
Interrupt Control Commands
The following seven LM628 user commands are associated with conditions which can be used to interrupt the host computer In order for any of the potential interrupt conditions to actually interrupt the host via Pin 17 the corresponding bit in the interrupt mask data associated with command MSKI must have been set to logic high (the non-masked state) The identity of all interrupts is made known to the host via reading and parsing the status byte Even if all interrupts are masked off via command MSKI the state of each condition is still reflected in the status byte This feature facilitates polling the LM628 for status information as opposed to interrupt driven operation SIP COMMAND Set Index Position Command Code 03 Hex Data Bytes None Executable During Motion Yes After this command is executed the absolute position which corresponds to the occurrence of the next index pulse input will be recorded in the index register and bit 3 of the status byte will be set to logic high The position is recorded when both encoder-phase inputs and the index pulse input are logic low This register can then be read by the user (see description for command RDIP) to facilitate aligning the definition of home position (see description of command DFH) with an index pulse The user can also arrange to have the LM628 interrupt the host to signify that an index pulse has occurred See the descriptions for commands MSKI and RSTI LPEI COMMAND Load Position Error for Interrupt Command Code 1B Hex Data Bytes Two Data Range 0000 to 7FFF Hex Executable During Motion Yes An excessive position error (the output of the loop summing junction) can indicate a serious system problem e g a stalled rotor Instruction LPEI allows the user to input a threshold for position error detection Error detection occurs when the absolute magnitude of the position error exceeds the threshold which results in bit 5 of the status byte being set to logic high If it is desired to also stop (turn off) the motor upon detecting excessive position error see command LPES below The first byte of threshold data written with command LPEI is the more significant The user can have the LM628 interrupt the host to signify that an excessive position error has occurred See the descriptions for commands MSKI and RSTI
Initialization Commands
The following four LM628 user commands are used primarily to initialize the system for use RESET COMMAND RESET the LM628 Command Code 00 Hex Data Bytes None Executable During Motion Yes This command (and the hardware reset input Pin 27) results in setting the following data items to zero filter coefficients and their input buffers trajectory parameters and their input buffers and the motor control output A zero motor control output is a half-scale offset-binary code (80 hex for the 8-bit output mode 800 hex for 12-bit mode) During reset the DAC port outputs 800 hex to ``zero'' a 12-bit DAC and reverts to 80 hex to ``zero'' an 8-bit DAC The command also clears five of the six interrupt masks (only the SBPA SBPR interrupt is masked) sets the output port size to 8 bits and defines the current absolute position as home Reset which may be executed at any time will be completed in less than 1 5 ms Also see commands PORT8 and PORT12 PORT8 COMMAND Set Output PORT Size to 8 Bits Command Code 05 Hex Data Bytes None Executable During Motion Not Applicable The default output port size of the LM628 is 8 bits so the PORT8 command need not be executed when using an 8-bit DAC This command must not be executed when using a 12-bit converter it will result in erratic unpredictable motor behavior The 8-bit output port size is the required selection when using the LM629 the PWM-output version of the LM628 PORT12 COMMAND Set Output PORT Size to 12 Bits Command Code 06 Hex Data Bytes None Executable During Motion Not Applicable When a 12-bit DAC is used command PORT12 should be issued very early in the initialization process Because use of this command is determined by system hardware there is only one foreseen reason to execute it later if the RESET command is issued (because an 8-bit output would then be selected as the default) command PORT12 should be im-
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Interrupt Control Commands (Continued)
LPES COMMAND Load Position Error for Stopping Command Code 1A Hex Data Bytes Two Data Range 0000 to 7FFF Hex Executable During Motion Yes Instruction LPES is essentially the same as command LPEI above but adds the feature of turning off the motor upon detecting excessive position error The motor drive is not actually switched off it is set to half-scale the offset-binary code for zero As with command LPEI bit 5 of the status byte is also set to logic high The first byte of threshold data written with command LPES is the more significant The user can have the LM628 interrupt the host to signify that an excessive position error has occurred See the descriptions for commands MSKI and RSTI SBPA COMMAND Command Code 20 Hex Data Bytes Four Data Range C0000000 to 3FFFFFFF Hex Executable During Motion Yes This command enables the user to set a breakpoint in terms of absolute position Bit 6 of the status byte is set to logic high when the breakpoint position is reached This condition is useful for signaling trajectory and or filter parameter updates The user can also arrange to have the LM628 interrupt the host to signify that a breakpoint position has been reached See the descriptions for commands MSKI and RSTI SBPR COMMAND Command Code 21 Hex Data Bytes Four Data Range See Text Executable During Motion Yes This command enables the user to set a breakpoint in terms of relative position As with command SBPA bit 6 of the status byte is set to logic high when the breakpoint position (relative to the current commanded target position) is reached The relative breakpoint input value must be such that when this value is added to the target position the result remains within the absolute position range of the system (C0000000 to 3FFFFFFF hex) This condition is useful for signaling trajectory and or filter parameter updates The user can also arrange to have the LM628 interrupt the host to signify that a breakpoint position has been reached See the descriptions for commands MSKI and RSTI MSKI COMMAND MaSK Interrupts Command Code 1C Hex Data Bytes Two Data Range See Text Executable During Motion Yes The MSKI command lets the user determine which potential interrupt condition(s) will interrupt the host Bits 1 through 6 of the status byte are indicators of the six conditions which are candidates for host interrupt(s) When interrupted the host then reads the status byte to learn which condition(s) occurred Note that the MSKI command is immediately followed by two data bytes Bits 1 through 6 of the second (less significant) byte written determine the masked unmasked status of each potential interrupt Any zero(s) in this 6-bit field will mask the corresponding interrupt(s) any one(s) enable the interrupt(s) Other bits comprising the two bytes have no effect The mask controls only the host interrupt process reading the status byte will still reflect the actual conditions independent of the mask byte See Table III TABLE III Mask and Reset Bit Allocations for Interrupts Bit Position Bits 15 thru 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Function Not Used Breakpoint Interrupt Position-Error Interrupt Wrap-Around Interrupt Index-Pulse Interrupt Trajectory-Complete Interrupt Command-Error Interrupt Not Used
RSTI COMMAND ReSeT Interrupts Command Code 1D Hex Data Bytes Two Data Range See Text Executable During Motion Yes When one of the potential interrupt conditions of Table III occurs command RSTI is used to reset the corresponding interrupt flag bit in the status byte The host may reset one or all flag bits Resetting them one at a time allows the host to service them one at a time according to a priority programmed by the user As in the MSKI command bits 1 through 6 of the second (less significant) byte correspond to the potential interrupt conditions shown in Table III Also see description of RDSTAT command Any zero(s) in this 6-bit field reset the corresponding interrupt(s) The remaining bits have no effect
Filter Control Commands
The following two LM628 user commands are used for setting the derivative-term sampling interval for adjusting the filter parameters as required to tune the system and to control the timing of these system changes LFIL COMMAND Load FILter Parameters Command Code 1E Hex Data Bytes Two to Ten Data Ranges Filter Control Word See Text Filter Coefficients 0000 to 7FFF Hex (Pos Only) Integration Limit 0000 to 7FFF Hex (Pos Only) Executable During Motion Yes The filter parameters (coefficients) which are written to the LM628 to control loop compensation are kp ki kd and il (integration limit) The integration limit (il) constrains the contribution of the integration term
n
ki
Ne0
e(n)
(see Eq 1) to values equal to or less than a user-defined maximum value this capability minimizes integral or reset ``wind-up'' (an overshooting effect of the integral action) The positive-only input value is compared to the absolute
(
12
Filter Control Commands (Continued)
magnitude of the integration term when the magnitude of integration term value exceeds il the il value (with appropriate sign) is substituted for the integration term value The derivative-term sampling interval is also programmable via this command After writing the command code the first two data bytes that are written specify the derivative-term sampling interval and which of the four filter parameters is are to be written via any forthcoming data bytes The first byte written is the more significant Thus the two data bytes constitute a filter control word that informs the LM628 as to the nature and number of any following data bytes See Table IV TABLE IV Filter Control word Bit Allocation Bit Position Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Function Derivative Sampling Interval Bit 7 Derivative Sampling Interval Bit 6 Derivative Sampling Interval Bit 5 Derivative Sampling Interval Bit 4 Derivative Sampling Interval Bit 3 Derivative Sampling Interval Bit 2 Derivative Sampling Interval Bit 1 Derivative Sampling Interval Bit 0 Not Used Not Used Not Used Not Used Loading kp Data Loading ki Data Loading kd Data Loading il Data The data bytes specified by and immediately following the filter control word are written in pairs to comprise 16-bit words The order of sending the data words to the LM628 corresponds to the descending order shown in the above description of the filter control word i e beginning with kp then ki kd and il The first byte of each word is the more-significant byte Prior to writing a word (byte pair) it is necessary to check the busy bit in the status byte for readiness The required data is written to the primary buffers of a double-buffered scheme by the above described operations it is not transferred to the secondary (working) registers until the UDF command is executed This fact can be used advantageously the user can input numerous data ahead of their actual use This simple pipeline effect can relieve potential host computer data communications bottlenecks and facilitates easier synchronization of multiple-axis controls UDF COMMAND UpDate Filter Command Code 04 Hex Data Bytes None Executable During Motion Yes The UDF command is used to update the filter parameters the specifics of which have been programmed via the LFIL command Any or all parameters (derivative-term sampling interval kp ki kd and or il) may be changed by the appropriate command(s) but command UDF must be executed to affect the change in filter tuning Filter updating is synchronized with the calculations to eliminate erratic or spurious behavior
Trajectory Control Commands
The following two LM628 user commands are used for setting the trajectory control parameters (position velocity acceleration) mode of operation (position or velocity) and direction (velocity mode only) as required to describe a desired motion or to select the mode of a manually directed stop and to control the timing of these system changes LTRJ COMMAND Load TRaJectory Parameters Command Code 1F Hex Data Bytes Two to Fourteen Data Ranges Trajectory Control Word See Text Position C0000000 to 3FFFFFFF Hex Velocity 00000000 to 3FFFFFFF Hex (Pos Only) Acceleration 00000000 to 3FFFFFFF Hex (Pos Only) Executable During Motion Conditionally See Text
Bits 8 through 15 select the derivative-term sampling interval See Table V The user must locally save and restore these bits during successive writes of the filter control word Bits 4 through 7 of the filter control word are not used Bits 0 to 3 inform the LM628 as to whether any or all of the filter parameters are about to be written The user may choose to update any or all (or none) of the filter parameters Those chosen for updating are so indicated by logic one(s) in the corresponding bit position(s) of the filter control word
TABLE V Derivative-Term Sampling Interval Selection Codes Bit Position 15 0 0 0 0 thru 1 14 0 0 0 0 1 13 0 0 0 0 1 12 0 0 0 0 1 11 0 0 0 0 1 10 0 0 0 0 1 9 0 0 1 1 1 8 0 1 0 1 1 Selected Derivative Sampling Interval 256 ms 512 ms 768 ms 1024 ms etc 65 536 ms
Note Sampling intervals shown are when using an 8 0 MHz clock The 256 corresponds to 2048 8 MHz sample intervals must be scaled for other clock frequencies
13
Trajectory Control Commands (Continued)
The trajectory control parameters which are written to the LM628 to control motion are acceleration velocity and position In addition indications as to whether these three parameters are to be considered as absolute or relative inputs selection of velocity mode and direction and manual stopping mode selection and execution are programmable via this command After writing the command code the first two data bytes that are written specify which parameter(s) is are being changed The first byte written is the more significant Thus the two data bytes constitute a trajectory control word that informs the LM628 as to the nature and number of any following data bytes See Table VI TABLE VI Trajectory Control Word Bit Allocation
Bit Position Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Not Used Not Used Not Used Forward Direction (Velocity Mode Only) Velocity Mode Stop Smoothly (Decelerate as Programmed) Stop Abruptly (Maximum Deceleration) Turn Off Motor (Output Zero Drive) Not Used Not Used Acceleration Will Be Loaded Acceleration Data Is Relative Velocity Will Be Loaded Velocity Data Is Relative Position Will Be Loaded Position Data Is Relative Function
Bit 12 determines the motor direction when in the velocity mode A logic one indicates forward direction This bit has no effect when in position mode Bit 11 determines whether the LM628 operates in velocity mode (Bit 11 logic one) or position mode (Bit 11 logic zero) Bits 8 through 10 are used to select the method of manually stopping the motor These bits are not provided for one to merely specify the desired mode of stopping in position mode operations normal stopping is always smooth and occurs automatically at the end of the specified trajectory Under exceptional circumstances it may be desired to manually intervene with the trajectory generation process to affect a premature stop In velocity mode operations however the normal means of stopping is via bits 8 through 10 (usually bit 10) Bit 8 is set to logic one to stop the motor by turning off motor drive output (outputting the appropriate offset-binary code to apply zero drive to the motor) bit 9 is set to one to stop the motor abruptly (at maximum available acceleration by setting the target position equal to the current position) and bit 10 is set to one to stop the motor smoothly by using the current user-programmed acceleration value Bits 8 through 10 are to be used exclusively only one bit should be a logic one at any time Bits 0 through 5 inform the LM628 as to whether any or all of the trajectory controlling parameters are about to be written and whether the data should be interpreted as absolute or relative The user may choose to update any or all (or
none) of the trajectory parameters Those chosen for updating are so indicated by logic one(s) in the corresponding bit position(s) Any parameter may be changed while the motor is in motion however if acceleration is changed then the next STT command must not be issued until the LM628 has completed the current move or has been manually stopped The data bytes specified by and immediately following the trajectory control word are written in pairs which comprise 16-bit words Each data item (parameter) requires two 16-bit words the word and byte order is most-to-least significant The order of sending the parameters to the LM628 corresponds to the descending order shown in the above description of the trajectory control word i e beginning with acceleration then velocity and finally position Acceleration and velocity are 32 bits positive only but range only from 0 (00000000 hex) to 230 b1 (3FFFFFFF hex) The bottom 16 bits of both acceleration and velocity are scaled as fractional data therefore the least-significant integer data bit for these parameters is bit 16 (where the bits are numbered 0 through 31) To determine the coding for a given velocity for example one multiplies the desired velocity (in counts per sample interval) times 65 536 and converts the result to binary The units of acceleration are counts per sample per sample The value loaded for acceleration must not exceed the value loaded for velocity Position is a signed 32-bit integer but ranges only from b 230 (C0000000 hex) to 230 b1 (3FFFFFFF Hex) The required data is written to the primary buffers of a double-buffered scheme by the above described operations it is not transferred to the secondary (working) registers until the STT command is executed This fact can be used advantageously the user can input numerous data ahead of their actual use This simple pipeline effect can relieve potential host computer data communications bottlenecks and facilitates easier synchronization of multiple-axis controls STT COMMAND STarT Motion Control Command Code 01 Hex Data Bytes None Executable During Motion Yes if acceleration has not been changed The STT command is used to execute the desired trajectory the specifics of which have been programmed via the LTRJ command Synchronization of multi-axis control (to within one sample interval) can be arranged by loading the required trajectory parameters for each (and every) axis and then simultaneously issuing a single STT command to all axes This command may be executed at any time unless the acceleration value has been changed and a trajectory has not been completed or the motor has not been manually stopped If STT is issued during motion and acceleration has been changed a command error interrupt will be generated and the command will be ignored
Data Reporting Commands
The following seven LM628 user commands are used to obtain data from various registers in the LM628 Status position and velocity information are reported With the exception of RDSTAT the data is read from the LM628 data port after first writing the corresponding command to the command port
14
Data Reporting Commands (Continued)
RDSTAT COMMAND ReaD STATus Byte Command Code None Byte Read One Data Range See Text Executable During Motion Yes The RDSTAT command is really not a command but is listed with the other commands because it is used very frequently to control communications with the host computer There is no identification code it is directly supported by the hardware and may be executed at any time The single-byte status read is selected by placing CS PS and RD at logic zero See Table VII TABLE VII Status Byte Bit Allocation Bit Position Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Function Motor Off Breakpoint Reached Interrupt Excessive Position Error Interrupt Wraparound Occurred Interrupt Index Pulse Observed Interrupt Trajectory Complete Interrupt Command Error Interrupt Busy Bit Bit 2 the trajectory complete interrupt flag is set to logic one when the trajectory programmed by the LTRJ command and initiated by the STT command has been completed Because of overshoot or a limiting condition (such as commanding the velocity to be higher than the motor can achieve) the motor may not yet be at the final commanded position This bit is the logical OR of bits 7 and 10 of the Signals Register see command RDSIGS below The flag functions independently of the host interrupt mask status Bit 2 is cleared via command RSTI Bit 1 the command-error interrupt flag is set to logic one when the user attempts to read data when a write was appropriate (or vice versa) The flag is functional independent of the host interrupt mask status Bit 1 is cleared via command RSTI Bit 0 the busy flag is frequently tested by the user (via the host computer program) to determine the busy ready status prior to writing and reading any data Such writes and reads may be executed only when bit 0 is logic zero (not busy) Any command or data writes when the busy bit is high will be ignored Any data reads when the busy bit is high will read the current contents of the I O port buffers not the data expected by the host Such reads or writes (with the busy bit high) will not generate a command-error interrupt RDSIGS COMMAND ReaD SIGnalS Register Command Code 0C Hex Bytes Read Two Data Range See Text Executable During Motion Yes The LM628 internal ``signals'' register may be read using this command The first byte read is the more significant The less significant byte of this register (with the exception of bit 0) duplicates the status byte See Table VIII TABLE VIII Signals Register Bit Allocation Bit Position Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Function Host Interrupt Acceleration Loaded (But Not Updated) UDF Executed (But Filter Not yet Updated) Forward Direction Velocity Mode On Target Turn Off upon Excessive Position Error Eight-Bit Output Mode Motor Off Breakpoint Reached Interrupt Excessive Position Error Interrupt Wraparound Occurred Interrupt Index Pulse Acquired Interrupt Trajectory Complete Interrupt Command Error Interrupt Acquire Next Index (SIP Executed)
Bit 7 the motor-off flag is set to logic one when the motor drive output is off (at the half-scale offset-binary code for zero) The motor is turned off by any of the following conditions power-up reset command RESET excessive position error (if command LPES had been executed) or when command LTRJ is used to manually stop the motor via turning the motor off Note that when bit 7 is set in conjunction with command LTRJ for producing a manual motor-off stop the actual setting of bit 7 does not occur until command STT is issued to affect the stop Bit 7 is cleared by command STT except as described in the previous sentence Bit 6 the breakpoint-reached interrupt flag is set to logic one when the position breakpoint loaded via command SBPA or SBPR has been exceeded The flag is functional independent of the host interrupt mask status Bit 6 is cleared via command RSTI Bit 5 the excessive-position-error interrupt flag is set to logic one when a position-error interrupt condition exists This occurs when the error threshold loaded via command LPEI or LPES has been exceeded The flag is functional independent of the host interrupt mask status Bit 5 is cleared via command RSTI Bit 4 the wraparound interrupt flag is set to logic one when a numerical ``wraparound'' has occurred To ``wraparound'' means to exceed the position address space of the LM628 which could occur during velocity mode operation If a wraparound has occurred then position information will be in error and this interrupt helps the user to ensure position data integrity The flag is functional independent of the host interrupt mask status Bit 4 is cleared via command RSTI Bit 3 the index-pulse acquired interrupt flag is set to logic one when an index pulse has occurred (if command SIP had been executed) and indicates that the index position register has been updated The flag is functional independent of the host interrupt mask status Bit 3 is cleared by command RSTI
Bit 15 the host interrupt flag is set to logic one when the host interrupt output (Pin 17) is logic one Pin 17 is set to logic one when any of the six host interrupt conditions occur (if the corresponding interrupt has not been masked) Bit 15 (and Pin 17) are cleared via command RSTI Bit 14 the acceleration-loaded flag is set to logic one when acceleration data is written to the LM628 Bit 14 is cleared by the STT command
15
Data Reporting Commands (Continued)
Bit 13 the UDF-executed flag is set to logic one when the UDF command is executed Because bit 13 is cleared at the end of the sampling interval in which it has been set this signal is very short-lived and probably not very profitable for monitoring Bit 12 the forward direction flag is meaningful only when the LM628 is in velocity mode The bit is set to logic one to indicate that the desired direction of motion is ``forward'' zero indicates ``reverse'' direction Bit 12 is set and cleared via command LTRJ The actual setting and clearing of bit 12 does not occur until command STT is executed Bit 11 the velocity mode flag is set to logic one to indicate that the user has selected (via command LTRJ) velocity mode Bit 11 is cleared when position mode is selected (via command LTRJ) The actual setting and clearing of bit 11 does not occur until command STT is executed Bit 10 the on-target flag is set to logic one when the trajectory generator has completed its functions for the last-issued STT command Bit 10 is cleared by the next STT command Bit 9 the turn-off on-error flag is set to logic one when command LPES is executed Bit 9 is cleared by command LPEI Bit 8 the 8-bit output flag is set to logic one when the LM628 is reset or when command PORT8 is executed Bit 8 is cleared by command PORT12 Bits 0 through 7 replicate the status byte (see Table VII) with the exception of bit 0 Bit 0 the acquire next index flag is set to logic one when command SIP is executed it then remains set until the next index pulse occurs RDIP COMMAND ReaD Index Position Command Code 09 Hex Bytes Read Four Data Range C0000000 to 3FFFFFFF Hex Executable During Motion Yes This command reads the position recorded in the index register Reading the index register can be part of a system error checking scheme Whenever the SIP command is executed the new index position minus the old index position divided by the incremental encoder resolution (encoder lines times four) should always be an integral number The RDIP command facilitates acquiring these data for hostbased calculations The command can also be used to identify verify home or some other special position The bytes are read in most-to-least significant order RDDP COMMAND ReaD Desired Position Command Code 08 Hex Bytes Read Four Data Range C0000000 to 3FFFFFFF Hex Executable During Motion Yes This command reads the instantaneous desired (current temporal ) position output of the profile generator This is the ``setpoint'' input to the position-loop summing junction The bytes are read in most-to-least significant order RDRP COMMAND ReaD Real Position Command Code 0A Hex Bytes Read Four Data Range C0000000 to 3FFFFFFF Hex Executable During Motion Yes This command reads the current actual position of the motor This is the feedback input to the loop summing junction The bytes are read in most-to-least significant order RDDV COMMAND ReaD Desired Velocity Command Code 07 Hex Bytes Read Four Data Range C0000001 to 3FFFFFFF Executable During Motion Yes This command reads the integer and fractional portions of the instantaneous desired (current temporal ) velocity as used to generate the desired position profile The bytes are read in most-to-least significant order The value read is properly scaled for numerical comparison with the user-supplied (commanded) velocity however because the two least-significant bytes represent fractional velocity only the two most-significant bytes are appropriate for comparison with the data obtained via command RDRV (see below) Also note that although the velocity input data is constrained to positive numbers (see command LTRJ) the data returned by command RDDV represents a signed quantity where negative numbers represent operation in the reverse direction RDRV COMMAND ReaD Real Velocity Command Code 0B Hex Bytes Read Two Data Range C000 to 3FFF Hex See Text Executable During Motion Yes This command reads the integer portion of the instantaneous actual velocity of the motor The internally maintained fractional portion of velocity is not reported because the reported data is derived by reading the incremental encoder which produces only integer data For comparison with the result obtained by executing command RDDV (or the user-supplied input value) the value returned by command RDRV must be multiplied by 216 (shifted left 16 bit positions) Also as with command RDDV above data returned by command RDRV is a signed quantity with negative values representing reverse-direction motion RDSUM COMMAND ReaD Integration-Term SUMmation Value Command Code 0D Hex Bytes Read Two Data Range 00000 Hex to g the Current Value of the Integration Limit Executable During Motion Yes This command reads the value to which the integration term has accumulated The ability to read this value may be helpful in initially or adaptively tuning the system
Typical Applications
Programming LM628 Host Handshaking (Interrupts) A few words regarding the LM628 host handshaking will be helpful to the system programmer As indicated in various portions of the above text the LM628 handshakes with the host computer in two ways via the host interrupt output (Pin 17) or via polling the status byte for ``interrupt'' conditions When the hardwired interrupt is used the status byte is also read and parsed to determine which of six possible conditions caused the interrupt
16
Typical Applications (Continued)
When using the hardwired interrupt it is very important that the host interrupt service routine does not interfere with a command sequence which might have been in progress when the interrupt occurred If the host interrupt service routine were to issue a command to the LM628 while it is in the middle of an ongoing command sequence the ongoing command will be aborted (which could be detrimental to the application) Two approaches exist for avoiding this problem If one is using hardwired interrupts they should be disabled at the host prior to issuing any LM628 command sequence and re-enabled after each command sequence The second approach is to avoid hardwired interrupts and poll the LM628 status byte for ``interrupt'' status The status byte always reflects the interrupt-condition status independent of whether or not the interrupts have been masked Typical Host Computer Processor Interface The LM628 is interfaced with the host computer processor via an 8-bit parallel bus Figure 12 shows such an interface and a minimum system configuration As shown in Figure 12 the LM628 interfaces with the host data address and control lines The address lines are decoded to generate the LM628 CS input the host address LSB directly drives the LM628 PS input Figure 12 also shows an 8-bit DAC and an LM12 Power Op Amp interfaced to the LM628 LM628 and High Performance Controller (HPC) Interface A Monolithic Linear Drive Using LM12 Power Op Amp Figure 15 shows a motor-drive amplifier built using the LM12 Power Operational Amplifier This circuit is very simple and can deliver up to 8A at 30V (using the LM12L LM12CL) Resistors R1 and R2 should be chosen to set the gain to provide maximum output voltage consistent with maximum input voltage This example provides a gain of 2 2 which allows for amplifier output saturation at g22V with a g10V input assuming power supply voltages of g30V The amplifier gain should not be higher than necessary because the system is non-linear when saturated and because gain should be controlled by the LM628 The LM12 can also be configured as a current driver see 1987 Linear Databook Vol 1 p 2 - 280 Typical PWM Motor Drive Interfaces Figure 16 shows an LM18298 dual full-bridge driver interfaced to the LM629 PWM outputs to provide a switch-mode power amplifier for driving small brush commutator motors Figure 17 shows an LM621 brushless motor commutator interfaced to the LM629 PWM outputs and a discrete device switch-mode power amplifier for driving brushless DC motors Incremental Encoder Interface The incremental (position feedback) encoder interface consists of three lines Phase A (Pin 2) Phase B (Pin 3) and Index (Pin 1) The index pulse output is not available on some encoders The LM628 will work with both encoder types but commands SIP and RDIP will not be meaningful without an index pulse (or alternative input for this input be sure to tie Pin 1 high if not used) Some consideration is merited relative to use in high Gaussian-noise environments If noise is added to the encoder inputs (either or both inputs) and is such that it is not sustained until the next encoder transition the LM628 decoder logic will reject it Noise that mimics quadrature counts or persists through encoder transitions must be eliminated by appropriate EMI design Simple digital ``filtering'' schemes merely reduce susceptibility to noise (there will always be noise pulses longer than the filter can eliminate) Further any noise filtering scheme reduces decoder bandwidth In the LM628 it was decided (since simple filtering does not eliminate the noise problem) to not include a noise filter in favor of offering maximum possible decoder bandwidth Attempting to drive encoder signals too long a distance with simple TTL lines can also be a source of ``noise'' in the form of signal degradation (poor risetime and or ringing) This can also cause a system to lose positional integrity Probably the most effective countermeasure to noise induction can be had by using balanced-line drivers and receivers on the encoder inputs Figure 18 shows circuitry using the DS26LS31 and DS26LS32
Figure 13 shows the LM628 interfaced to a National HPC High Performance Controller The delay and logic associated with the WR line is used to effectively increase the writedata hold time of the HPC (as seen at the LM628) by causing the WR pulse to rise early Note that the HPC CK2 output provides the clock for the LM628 The 74LS245 is used to decrease the read-data hold time which is necessary when interfacing to fast host busses
Interfacing a 12-Bit DAC Figure 14 illustrates use of a 12-bit DAC with the LM628 The 74LS378 hex gated-D flip-flop and an inverter demultiplex the 12-bit output DAC offset must be adjusted to minimize DAC linearity and monotonicity errors Two methods exist for making this adjustment If the DAC1210 has been socketed remove it and temporarily connect a 15 kX resistor between Pins 11 and 13 of the DAC socket (Pins 2 and 6 of the LF356) and adjust the 25 kX potentiometer for 0V at Pin 6 of the LF356 If the DAC is not removable the second method of adjustment requires that the DAC1210 inputs be presented an allzeros code This can be arranged by commanding the appropriate move via the LM628 but with no feedback from the system encoder When the all-zeros code is present adjust the pot for 0V at Pin 6 of the LF356
17
Typical Applications (Continued)
Note AV e
R1 a R2 R1
24
R1 c R2 D e 2 5k R1 a R2
TL H 9219 - 14
FIGURE 12 Host Interface and Minimum System Configuration
TL H 9219 - 15
FIGURE 13 LM628 and HPC Interface
18
Typical Applications (Continued)
19
TL H 9219 - 16
DAC offset must be adjusted to minimize DAC linearity and monotonicity errors See text
FIGURE 14 Interfacing a 12-Bit DAC and LM628
Typical Applications (Continued)
TL H 9219 - 17
FIGURE 15 Driving a Motor with the LM12 Power Op Amp
TL H 9219 - 18
FIGURE 16 PWM Drive for Brush Commutator Motors
20
Typical Applications (Continued)
TL H 9219 - 19
FIGURE 17 PWM Drive for Brushless Motors
TL H 9219 - 20
FIGURE 18 Typical Balanced-Line Encoder Input Circuit
21
22
Physical Dimensions inches (millimeters)
24-Lead Small Outline Package (M) Order Number LM629M-6 or LM629M-8 NS Package Number M24B
23
LM628 LM629 Precision Motion Controller
Physical Dimensions inches (millimeters) (Continued)
28 Lead Molded Dual-In-Line Package (N) Order Number LM628N-6 LM628N-8 LM629N-6 or LM629N-8 NS Package Number N28B
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