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?2009 integrated device technology, inc. january 2009 dsc 2621/13 1 idt71342sa/la high speed 4k x 8 dual-port static ram with semaphore features high-speed access ? commercial: 20/25/35/45/55/70ns (max.) ? industrial: 25/35/55ns (max.) low-power operation ? idt71342sa active: 700mw (typ.) standby: 5mw (typ.) ? idt71342la active: 700mw (typ.) standby: 1mw (typ.) functional block diagram 2721 drw 01 i/o control i/o control memory array address decoder address decoder r/ w r ce r oe r i/o 0r -i/o 7r a 0r -a 11r r/ w l ce l oe l a 0l -a 11l i/o 0l -i/o 7l semaphore logic sem r sem l fully asynchronous operation from either port full on-chip hardware support of semaphore signalling be- tween ports battery backup operation?2v data retention (la only) ttl-compatible; single 5v (10%) power supply available in plastic packages industrial temperature range (?40c to +85c) is available for selected speeds
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperature ranges 2 2721 drw 02 idt71342j j52-1 (4) 52-pin plcc top view (5) index n / c g n d i / o 4 l i / o 5 l i / o 6 l i / o 7 l i / o 0 r i / o 1 r i / o 2 r i / o 3 r i / o 4 r i / o 5 r i / o 6 r oe r a 0r a 1r a 2r a 3r a 4r a 5r a 6r a 7r a 8r a 9r n/c i/o 7r 46 45 44 43 42 41 40 39 38 37 36 35 34 i/o 3l a 1l a 2l a 3l a 4l a 5l a 6l a 7l a 8l a 9l i/o 0l i/o 1l i/o 2l 8 9 10 11 12 13 14 15 16 17 18 19 20 47 48 49 50 51 52 1 2 3 4 5 6 7 33 32 31 30 29 28 27 26 25 24 23 22 21 s e m l a 0 l v c c o e l r / w l c e r r / w r c e l a 1 0 l a 1 1 l a 1 0 r a 1 1 r s e m r notes: 1. all vcc pins must be connected to power supply. 2. all gnd pins must be connected to ground supply. 3. j52 package body is approximately .79 in x .79 in x .17 in. pn64 package body is approximately 14mm x 14mm x 1.4mm. 4. this package code is used to reference the package diagram. 5. this text does not indicate orientation of the actual part-marking. pin configurations (1,2,3) i ndex 71342pf pn64-1 (4) 64-pin tqfp top view (5) 8 9 10 11 12 13 14 15 16 1 2 3 4 5 6 7 46 45 44 43 42 41 40 39 38 37 36 35 34 47 48 33 1 7 1 8 1 9 2 0 3 2 3 1 3 0 2 9 2 8 2 7 2 6 2 5 2 4 2 3 2 2 2 1 4 9 5 0 5 1 5 2 6 3 6 2 6 1 6 0 5 9 5 8 5 7 5 6 5 5 5 4 5 3 6 4 i/o 6r n/c a 0r a 1r a 2r a 3r a 4r a 5r a 6r a 7r a 8r a 9r i/o 7r oe r n/c n/c i/o 2l a 0l oe l a 1l a 2l a 3l a 4l a 5l a 6l a 7l a 8l a 9l i/o 0l i/o 1l n/c n/c i / o 4 l i / o 5 l i / o 6 l i / o 7 l i / o 0 r i / o 1 r i / o 2 r i / o 3 r i / o 4 r i / o 5 r i / o 3 l n / c n / c g n d n / c n / c a 1 0 r v c c c e r c e l n / c n / c a 1 0 l n / c n / c n / c a 1 1 l a 1 1 r 2721 drw 03 s e m l r / w l s e m r r / w r , description the idt71342 is a high-speed 4k x 8 dual-port static ram with full on-chip hardware support of semaphore signalling between the two ports. the idt71342 provides two independent ports with separate control, address, and i/o pins that permit independent, asynchronous access for reads or writes to any location in memory. to assist in arbitrating between ports, a fully independent semaphore logic block is provided. this block contains unassigned flags which can be accessed by either side; however, only one side can control the flag at any time. an automatic power down feature, controlled by ce and sem , permits the on-chip circuitry of each port to enter a very low standby power mode (both ce and sem high). fabricated using idt?s cmos high-performance technology, this device typically operates on only 700mw of power. low-power (la) versions offer battery backup data retention capability, with each port typically consuming 200w from a 2v battery. the device is packaged in either a 64-pin tqfp or a 52-pin plcc.
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperatu re ranges 3 absolute maximum ratings (1) capacitance (1) (t a = +25c, f = 1.0mhz) maximum operating temperature and supply voltage (1,2) recommended dc operating conditions notes: 1. stresses greater than those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect reliability. 2. v term must not exceed vcc + 10% for more than 25% of the cycle time or 10 ns maximum, and is limited to < 20ma for the period of v term > vcc +10%. notes: 1. this parameter is determined by device characterization but is not production tested. 2. 3dv references the interpolated capacitance when the input and output signals switch from 0v to 3v and from 3v to 0v. notes: 1. this is the parameter t a . this is the "instant on" case temperature. notes: 1. v il (min.) > -1.5v for pulse width less than 10ns. 2. v term must not exceed vcc + 10%. note: 1. at vcc < 2.0v input leakages are undefined. dc electrical characteristics over the operating temperature and supply voltage (v cc = 5v 10%) symbol rating commercial & industrial unit v te rm (2 ) terminal voltage with respect to gnd -0.5 to +7.0 v t bias temperature under bias -55 to +125 o c t stg storage temperature -65 to +150 o c p t (3) power dissipation 1.5 w i out dc output current 50 ma 2721 tbl 01 symbol parameter conditions (2 ) max. unit c in input capacitance v in = 3dv 9 pf c out output capacitance v out = 3dv 10 pf 2721 tbl 02 grade ambient temperature gnd vcc commercial 0 o c to +70 o c0v5.0v + 10% industrial -40 o c to +85 o c0v5.0v + 10% 27 21 tb l 03 symbol parameter min. typ. max. unit v cc supply voltage 4.5 5.0 5.5 v gnd ground 0 0 0 v v ih input high voltage 2.2 ____ 6.0 (2 ) v v il input low voltage -0.5 (1 ) ____ 0.8 v 2721 tbl 04 symbol parameter test conditions 71342sa 71342la unit min. max. min. max. |i li | input leakage current (1 ) v cc = 5.5v, v in = 0v to v cc ___ 10 ___ 5a |i lo | output leakage current ce = v ih , v out = 0v to v cc ___ 10 ___ 5a v ol output low voltage i ol = 6ma ___ 0.4 ___ 0.4 v i ol = 8ma ___ 0.5 ___ 0.5 v v oh output high voltage i oh = -4ma 2.4 ___ 2.4 ___ v 2721 tb l 0 5
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperature ranges 4 dc electrical characteristics over the operating temperature and supply voltage range (1) (v cc = 5.0v 10%) notes: 1. 'x' in part number indicates power rating (sa or la). 2. v cc = 5v, t a = +25c for typical, and parameters are not production tested. 3. f max = 1/t rc = all inputs cycling at f = 1/t rc (except output enable). f = 0 means no address or control lines change. applies only to inputs at cmos level standby i sb3. 71342x20 com'l only 71342x25 com'l & ind 71342x35 com'l & ind symbol parameter test condition version typ. (2 ) max. typ. (2) max. typ. (2) max. unit i cc dynamic operating current (both ports active) ce = v il , outputs disabled sem = don't care f = f max (3) com'l sa la 170 170 280 240 160 160 280 240 150 150 260 200 ma ind sa la ____ ____ ____ ____ 160 160 310 260 150 150 300 250 i sb1 standby current (both ports - ttl level inputs) ce l and ce r = v ih sem l = sem r > v ih f = f max (3) com'l sa la 25 25 80 80 25 25 80 50 25 25 75 45 ma ind sa la ____ ____ ____ ____ 25 25 100 80 25 25 75 55 i sb2 standby current (one port - ttl level inputs) ce "a " = v il and ce "b" = v ih active port outputs disabled, f=f max (3 ) com'l sa la 105 105 180 150 95 95 180 150 85 85 170 140 ma ind sa la ____ ____ ____ ____ 95 95 210 170 85 85 200 160 i sb3 full stand by current (both ports - cmos le vel inputs) both ports ce l and ce r > v cc - 0.2v, v in > v cc - 0.2v or v in < 0.2v sem l = sem r > v cc - 0.2v f = 0 (3 ) com'l sa la 1.0 0.2 15 4.5 1.0 0.2 15 4.0 1.0 0.2 15 4.0 ma ind sa la ____ ____ ____ ____ 1.0 0.2 30 10 1.0 0.2 30 10 i sb4 full standby current (one po rt - cmos le vel inputs) one port ce "a" or ce "b " > v cc - 0.2v v in > v cc - 0.2v or v in < 0.2v sem l = sem r > v cc - 0.2v active port outputs disabled, f = f max (3) com'l sa la 105 105 170 130 95 95 170 120 85 85 150 110 ma ind sa la ____ ____ ____ ____ 95 95 210 190 85 85 190 130 2721 tbl 06a 71342x45 com'l only 71342x55 com'l & ind 71342x70 com'l only symbol parameter test condition version typ. (2 ) max. typ. (2) max. typ. (2 ) max. unit i cc dynamic operating current (both ports active) ce = v il , outputs disabled sem = don't care f = f max (3 ) com'l sa la 140 140 240 200 140 140 240 200 140 140 240 200 ma ind sa la ____ ____ ____ ____ 140 140 270 220 ____ ____ ____ ____ i sb1 standby current (both ports - ttl level inputs) ce l and ce r = v ih sem l = sem r > v ih f = f max (3 ) com'l sa la 25 25 70 40 25 25 70 40 25 25 70 40 ma ind sa la ____ ____ ____ ____ 25 25 70 50 ____ ____ ____ ____ i sb2 standby current (one port - ttl level inputs) ce "a " = v il and ce "b" = v ih active port outputs disabled, f=f max (3) com'l sa la 75 75 160 130 75 75 160 130 75 75 160 130 ma ind sa la ____ ____ ____ ____ 75 75 180 150 ____ ____ ____ ____ i sb3 full standby current (both ports - cmos level inputs) both ports ce l and ce r > v cc - 0.2v, v in > v cc - 0.2v or v in < 0.2v sem l = sem r > v cc - 0.2 v f = 0 (3 ) com'l sa la 1.0 0.2 15 4.0 1.0 0.2 15 4.0 1.0 0.2 15 4.0 ma ind sa la ____ ____ ____ ____ 1.0 2.0 30 10 ____ ____ ____ ____ i sb4 full standby current (one port - cmos level inputs) one port ce "a" or ce "b " > v cc - 0.2v v in > v cc - 0.2v or v in < 0.2v sem l = sem r > v cc - 0.2v active port outputs disabled, f = f max (3 ) com'l sa la 75 75 150 100 75 75 150 100 75 75 150 100 ma ind sa la ____ ____ ____ ____ 75 75 170 120 ____ ____ ____ ____ 2721 tb l 06b
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperatu re ranges 5 data retention characteristics (la version only) v lc = 0.2v, v hc = v cc - 0.2v data rention waveform ac test conditions figure 2. output test load (for t lz , t hz , t wz , t ow ) *including scope and jig figure 1. ac output test load notes: 1. v cc = 2v, t a = +25c, and are not production tested. 2. t rc = read cycle time. 3. this parameter is guaranteed by device characterization, but is not production tested. symbol parameter test condition min. typ. (1 ) max. unit v dr v cc fo r data re te ntio n ___ 2.0 ___ v i ccdr data retention current v cc = 2v, ce > v hc com'l. & ind. ___ 100 1500 a t cd r (3 ) chip dese lect to data retention time sem > v hc v in > v hc or < v lc 0 ___ ___ ns t r (3 ) operation recovery time t rc (2 ) ___ ___ ns 2721 tbl 07 input pulse levels input rise/fall times input timing reference levels output reference levels output load gnd to 3.0v 5ns 1.5v 1.5v fi gures 1 and 2 2721 tbl 08 v cc ce d a t a r e t e n t i o n m o d e 4.5v 4.5v v dr > 2v v dr v ih v ih t cdr t r 2721 drw 04 +5v 1250 ? 30pf 775 ? data out 2721 drw 05 , +5v 1250 ? 5pf * 775 ? data out 2721 drw 06 ,
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperature ranges 6 ac electrical characteristics over the operating temperature and supply voltage (5) notes: 1. transition is measured 0mv from low or high-impedance voltage with the ouput test load (figure 2). 2. this parameter is guaranteed by device characterization, but is not production tested. 3. to access sram, ce = v il, sem = v ih . to access semaphore, ce = v ih , and sem = v il . 4. 'x' in part number indicates power rating (sa or la). 5. port-to-port delay through ram cells from writing port to reading port, refer to ?timing waveform of write with port-to-port read?. 71342x20 com'l only 71342x25 com'l & ind 71342x35 com'l & ind unit symbol parameter min.max.min.max.min.max. read cycle t rc read cycle time 20 ____ 25 ____ 35 ____ ns t aa address access time ____ 20 ____ 25 ____ 35 ns t ace chip enable access time (3) ____ 20 ____ 25 ____ 35 ns t aoe output enable access time ____ 15 ____ 15 ____ 20 ns t oh output hold from address change 0 ____ 0 ____ 0 ____ ns t lz output low-z time (1,2) 0 ____ 0 ____ 0 ____ ns t hz output high-z time (1,2) ____ 15 ____ 15 ____ 20 ns t pu chip enable to power up time (2 ) 0 ____ 0 ____ 0 ____ ns t pd chip disable to power down time (2) ____ 50 ____ 50 ____ 50 ns t sop sem flag update pulse ( oe or sem ) 10 ____ 10 ____ 15 ____ ns t wdd write pulse to data delay (4) ____ 40 ____ 50 ____ 60 ns t dd d write data valid to read data delay (4 ) ____ 30 ____ 30 ____ 35 ns t sa a semaphore address access time ____ ____ ____ 25 ____ 35 ns 2721 tbl 09a 71342x45 com'l only 71342x55 com'l & ind 71342x70 com'l only unit symbol parameter min.max.min.max.min.max. read cycle t rc re ad cycle time 45 ____ 55 ____ 70 ____ ns t aa address access time ____ 45 ____ 55 ____ 70 ns t ace chip enable access time (3) ____ 45 ____ 55 ____ 70 ns t aoe output enable access time ____ 25 ____ 30 ____ 40 ns t oh output hold from address change 0 ____ 0 ____ 0 ____ ns t lz output low-z time (1,2) 5 ____ 5 ____ 5 ____ ns t hz output high-z time (1,2) ____ 20 ____ 25 ____ 30 ns t pu chip enable to power up time (2 ) 0 ____ 0 ____ 0 ____ ns t pd chip disable to power down time (2 ) ____ 50 ____ 50 ____ 50 ns t sop sem flag update pulse ( oe or sem ) 15 ____ 20 ____ 20 ____ ns t wdd write pulse to data delay (4 ) ____ 70 ____ 80 ____ 90 ns t dd d write data valid to read data delay (4) ____ 45 ____ 55 ____ 70 ns t sa a semaphore address access time ____ 45 ____ 55 ____ 70 ns 2721 tbl 09b
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperatu re ranges 7 timing waveform of read cycle no. 1, either side (1,2,4) notes: 1. write cycle parameters should be adhered to, in order to ensure proper writing. 2. ce l = ce r = v il. ce "b" = v il. 3. port "a" may be either left or right port. port "b" is the opposite from port "a". timing waveform of read cycle no. 2, either side (1,3) timing waveform of write with port-to-port read (2,3) notes: 1. timing depends on which signal is asserted last, oe or ce . 2. timing depends on which signal is de-asserted first, oe or ce . 3. r/ w = v ih and oe = v il , unless otherwise noted. 4. start of valid data depends on which timing becomes effective last; t aoe , t ace , or t aa 5. to access sram, ce = v il and sem = v ih . to access semaphore, ce = v ih and sem = v il . t aa is for sram address access and t saa is for semaphore address access. t aa or t saa address data out previous data valid data valid t oh t oh t rc 2721 drw 07 2721 drw 08 ce or sem data out valid data t pd t aoe t ace oe t hz t lz t lz t pu 50% 50% i cc i sb current t hz t sop (5) t sop (1) (1) (4) (2) (2) (4) 2721 drw 09 r/ w "a" valid t wc match valid match t wp t dw t wdd t ddd addr "a" data in "a" data out "b" addr "b" (1) t dh
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperature ranges 8 ac electrical characteristics over the operating temperature supply voltage (5) notes: 1. transition is measured 0mv from low or high-impedance voltage with output test load (figure 2). 2. this parameter is guaranteed by device characterization but is not production tested. 3. to access sram, ce = v il and sem = v ih . to access semaphore, ce = v ih and sem = v il. either condition must be valid for the entire t ew time. 4. the specification for t dh must be met by the device supplying write data to the sram under all operating conditions. although t dh and t ow values will vary over voltage and temperature, the actual t dh will always be smaller than the actual t ow . 5. 'x' in part number indicates power rating (sa or la). symbol parameter 71342x20 com'l only 71342x25 com'l & ind 71342x35 com'l & ind unit min. max. min. max. min. max. writ e cycle t wc write cycle time 20 ____ 25 ____ 35 ____ ns t ew chip enable to end-of-write (3) 15 ____ 20 ____ 30 ____ ns t aw address valid to end-of-write 15 ____ 20 ____ 30 ____ ns t as address set-up time 0 ____ 0 ____ 0 ____ ns t wp write pulse width 15 ____ 20 ____ 25 ____ ns t wr write recovery time 0 ____ 0 ____ 0 ____ ns t dw data valid to end-of-write 15 ____ 15 ____ 20 ____ ns t hz output high-z time (1,2) ____ 15 ____ 15 ____ 20 ns t dh data ho ld time (4 ) 0 ____ 0 ____ 3 ____ ns t wz write enable to output in high-z (1,2) ____ 15 ____ 15 ____ 20 ns t ow output active from end-of-write (1 , 2,4 ) 3 ____ 3 ____ 3 ____ ns t swr sem flag write to read time 10 ____ 10 ____ 10 ____ ns t sp s sem flag contention window 10 ____ 10 ____ 10 ____ ns 2721 tbl 10a symbol parameter 71342x45 com'l only 71342x55 com'l & ind 71342x70 com'l only unit min. max. min. max. min. max. writ e cycle t wc write cycle time 45 ____ 55 ____ 70 ____ ns t ew chip enable to end-of-write (3) 40 ____ 50 ____ 60 ____ ns t aw address valid to end-of-write 40 ____ 50 ____ 60 ____ ns t as address set-up time 0 ____ 0 ____ 0 ____ ns t wp write pulse width 40 ____ 50 ____ 60 ____ ns t wr write recovery time 0 ____ 0 ____ 0 ____ ns t dw data valid to end-of-write 20 ____ 25 ____ 30 ____ ns t hz output high-z time (1,2) ____ 20 ____ 25 ____ 30 ns t dh data ho ld time (4 ) 3 ____ 3 ____ 3 ____ ns t wz write enable to output in high-z (1,2) ____ 20 ____ 25 ____ 30 ns t ow output active from end-of-write (1 , 2,4 ) 3 ____ 3 ____ 3 ____ ns t swr sem flag write to read time 10 ____ 10 ____ 10 ____ ns t sp s sem flag contention window 10 ____ 10 ____ 10 ____ ns 2721 tbl 10b
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperatu re ranges 9 ce or sem 2721 drw 10 t aw t as t wr t dw data in address t wc r/ w t wp t dh data out t wz (4) (4) t ow oe t hz t lz t hz (9) (6) (7) (2) (3) (7) (7) timing waveform of write cycle no. 1, r/ w w w w w controlled timing (1,5,8) timing waveform of write cycle no. 2, ce controlled timing (1, 5) notes: 1. r/ w or ce must be high during all address transitions. 2. a write occurs during the overlap (t ew or t wp ) of either ce or sem = v il and r/ w = v il . 3. t wr is measured from the earlier of ce or r/ w going high to the end-of-write cycle. 4. during this period, the i/o pins are in the output state, and input signals must not be applied. 5. if the ce low transition occurs simultaneously with or after the r/ w low transition, the outputs remain in the high-impedance state. 6. timing depends on which enable signal ( ce or r/ w ) is asserted last. 7. this parameter is guaranteed by device characterization, but is not production tested. transition is measured 0mv from steady state with the output test load (figure 2). 8. if oe is low during a r/ w controlled write cycle, the write pulse width must be the larger of t wp or (t wz + t dw ) to allow the i/o drivers to turn off data to be placed on the bus for the required t dw . if oe is high during an r/ w controlled write cycle, this requirement does not apply and the write pulse can be as short as the specified t wp . 9. to access sram, ce =v il and sem = v ih . to access semaphore, ce = v ih and sem = v il . either condition must be valid for the entire t ew time. 2721 drw 11 r/ w t wc address data in ce or sem t dw t wr t dh t ew t as t aw (9) (6) (2) (3)
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperature ranges 10 timing waveform of semaphore read after write timing, either side (1) note: 1. ce = v ih for the duration of the above timing (both write and read cycle). notes: 1. d 0r = d 0l = v il , ce r = ce l = v ih , semaphore flag is released from both sides (reads as ones from both sides) at cycle start. 2. all timing is the same for left and right ports. port "a" may be either left or right port. port "b" is the opposite from por t "a". 3. this parameter is measured from the point where r/ w " a " or sem " a " goes high until r/ w " b " or sem " b " goes high. 4. if t sps is violated, the semaphore will fall positively to one side or the other, but there is no guarantee which side will obtain the flag. timing waveform of semaphore condition (1,3,4) a 0 -a 2 valid address valid address data in valid data out valid sem r/ w oe data 0 t aw t ew t wr t dw t dh t wp t as t swrd t sop t aoe t ace t saa t oh t sop test cycle (read cycle) write cycle 2721 drw 12 a 0"a" -a 2"a" t sps r/ w "a" sem "a" side (2) "a" a 0"b" -a 2"b" r/ w " b " sem "b" side (2) "b" match match 2721 drw 13
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperatu re ranges 11 functional description the idt71342 is an extremely fast dual-port 4k x 8 cmos static ram with an additional 8 address locations dedicated to binary semaphore flags. these flags allow either processor on the left or right side of the dual-port ram to claim a privilege over the other processor for functions defined by the system designer?s software. as an example, the semaphore can be used by one processor to inhibit the other from accessing a portion of the dual-port ram or any other shared resource. the dual-port ram features a fast access time, and both ports are completely independent of each other. this means that the activity on the left port in no way slows the access time of the right port. both ports are identical in function to standard cmos static rams and can be read from or written to at the same time, with the only possible conflict arising from the simultaneous writing of, or a simultaneous read/ write of, a non-semaphore location. semaphores are protected against such ambiguous situations and may be used by the system program to avoid any conflicts in the non-semaphore portion of the dual-port sram. these devices have an automatic power-down feature controlled by ce , the dual-port sram enable, and sem , the semaphore enable. the ce and sem pins control on-chip power down circuitry that permits the respective port to go into standby mode when not selected. this is the condition which is shown in truth table i where ce and sem are both high. systems which can best use the idt71342 contain multiple processors or controllers and are typically very high-speed systems which are software controlled or software intensive. these systems can benefit from a performance increase offered by the idt71342?s hardware semaphores, which provide a lockout mechanism without requiring complex programming. software handshaking between processors offers the maximum in system flexibility by permitting shared resources to be allocated in varying configurations. the idt71342 does not use its semaphore flags to control any resources through hardware, thus allowing the system designer total flexibility in system architecture. an advantage of using semaphores rather than the more common methods of hardware arbitration is that wait states are never incurred in either processor. this can prove to be a major advantage in very high-speed systems. how the semaphore flags work the semaphore logic is a set of eight latches which are independent of the dual-port ram. these latches can be used to pass a flag, or token, from one port to the other to indicate that a shared resource is in use. the semaphores provide a hardware assist for a use assignment method called ?token passing allocation.? in this method, the state of a semaphore latch is used as a token indicating that a shared resource is in use. if the left processor wants to use this resource, it requests the token by setting the latch. this processor then verifies its success in setting the latch by reading it. if it was successful, it proceeds to assume control over the shared resource. if it was not successful in setting the latch, it determines that the right side processor had set the latch first, has the token and is using the shared resource. the left processor can then either repeatedly request that semaphore?s status or remove its request for that semaphore to perform another task and occasionally attempt again to gain control of the token via the set and test sequence. once the right side has relinquished the token, the left side should succeed in gaining control. the semaphore flags are active low. a token is requested by writing a zero into a semaphore latch and is released when the same side writes a one to that latch. the eight semaphore flags reside within the idt71342 in a separate memory space from the dual-port ram. this address space is accessed by placing a low input on the sem pin (which acts as a chip select for the semaphore flags) and using the other control pins (address, oe , and r/ w ) as they would be used in accessing a standard static ram. each of the flags has a unique address which can be accessed by either side through the address pins a 0 ?a 2 . when accessing the semaphores, none of the other address pins has any effect. when writing to a semaphore, only data pin d 0 is used. if a low level is written into an unused semaphore location, that flag will be set to a zero on that side and a one on the other (see truth table ii). that semaphore can now only be modified by the side showing the zero. when a one is written into the same location from the same side, the flag will be set to a one for both sides (unless a semaphore request from the other side is pending) and then can be written to by both sides. the fact that the side which is able to write a zero into a semaphore subsequently locks out writes from the other side is what makes semaphore flags useful in interprocessor communications. (a thorough discussion on the use of this feature follows shortly.) a zero written into the same location from the other side will be stored in the semaphore request latch for that side until the semaphore is freed by the first side. when a semaphore flag is read, its value is spread into all data bits so that a flag that is a one reads as a one in all data bits and a flag containing a zero reads as all zeros. the read value is latched into one side?s output register when that side?s semaphore select ( sem ) and output enable ( oe ) signals go active. this serves to disallow the semaphore from changing state in the middle of a read cycle due to a write cycle from the other side. because of this latch, a repeated read of a semaphore in a test loop must cause either signal ( sem or oe ) to go inactive or the output will never change. a sequence of write/read must be used by the semaphore in order to guarantee that no system level contention will occur. a processor requests access to shared resources by attempting to write a zero into a semaphore location. if the semaphore is already in use, the semaphore request latch will contain a zero, yet the semaphore flag will appear as a one, a fact which the processor will verify by the subsequent read (see truth table ii). as an example, assume a processor writes a zero in the left port at a free semaphore location. on a subsequent read, the processor will verify that it has written successfully to that location and will assume control over the resource in question. meanwhile, if a processor on the right side attempts to write a zero to the same semaphore flag it will fail, as will be verified by the fact that a one will be read from that semaphore on the right side during a subsequent read. had a sequence of read/write been used instead, system contention problems could have occurred during the gap between the read and write cycles. it is important to note that a failed semaphore request must be followed by either repeated reads or by writing a one into the same location. the reason for this is easily understood by looking at the simple logic diagram of the semaphore flag in figure 3. two semaphore
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperature ranges 12 truth table i ? non-contention read/write control (2) request latches feed into a semaphore flag. whichever latch is first to present a zero to the semaphore flag will force its side of the semaphore flag low and the other side high. this condition will continue until a one is written to the same semaphore request latch. should the other side?s semaphore request latch have been written to a zero in the meantime, the semaphore flag will now stay low until its semaphore request latch is written to a one. from this it is easy to understand that, if a semaphore is requested and the processor which requested it no longer needs the resource, the entire can hang up until a one is written into that semaphore request latch. the critical case of semaphore timing is when both sides request a single token by attempting to write a zero into it at the same time. the semaphore logic is specially designed to resolve this problem. if simultaneous requests are made, the logic guarantees that only one side receives the token. if one side is earlier than the other in making the request, the first side to make the request will receive the token. if both requests arrive at the same time, the assignment will be arbitrarily made to one port or the other. one caution that should be noted when using semaphores is that semaphores alone do not guarantee that access to a resource is secure. as with any powerful programming technique, if semaphores are misused or misinterpreted, a software error can easily happen. code integrity is of the utmost importance when semaphores are used instead of slower, more restrictive hardware intensive schemes. initialization of the semaphores is not automatic and must be handled via the initialization program at power up. since any semaphore request flag which contains a zero must be reset to a one, all truth table ii ? example semaphore procurement sequence (1,2,3) note: 1. a ol = a 11l 1 a 0r - a 11r. 2. "h" = v ih , "l" = v il , "x" = don?t care, "z" = high-impedance. note: 1. this table denotes a sequence of events for only one of the eight semaphores on the idt71342. 2. there are eight semaphore flags written to via i/o 0 and read from all i/o's. these eight semaphores are addressed by a 0 -a 2 . 3. ce = vih, sem = vil to access the semaphores. refer to the semaphore read/write control truth table. left or right port (1 ) r/ w ce sem oe d 0-7 function x h h x z port disab led and in power down mode hhl ldata out data in semaphore flag output on port x x x h z output disabled hlxdata in port data bit d 0 written into semaphore flag hlhldata out data in memory output on port llhxdata in data on port written into memory xllx ____ not allowed 2721 tbl 1 1 functions d 0 - d 15 left d 0 - d 15 right status no action 1 1 semaphore free left port writes "0" to semaphore 0 1 left port has semaphore token right port writes "0" to semaphore 0 1 no change. right side has no write access to semaphore left port writes "1" to semaphore 1 0 right port obtains semaphore token left port writes "0" to semaphore 1 0 no change. left port has no write access to semaphore right port writes "1" to semaphore 0 1 left port obtains semaphore token left port writes "1" to semaphore 1 1 semaphore free right port writes "0" to semaphore 1 0 right port has semaphore token right port writes "1" to semaphore 1 1 semaphore free left port writes "0" to semaphore 0 1 left port has semaphore token left port writes "1" to semaphore 1 1 semaphore free 2721 tbl 12
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperatu re ranges 13 semaphore request flip flop dq semaphore request flip flop qd write d 0 semaphore read semaphore read d 0 write rport lport 2721 drw 14 , semaphores on both sides should have a one written into them at initialization from both sides to assure that they will be free when needed. using semaphores?some examples perhaps the simplest application of semaphores is their application as resource markers for the idt71342?s dual-port ram. say the 4k x 8 ram was to be divided into two 2k x 8 blocks which were to be dedicated at any one time to servicing either the left or right port. semaphore 0 could be used to indicate the side which would control the lower section of memory, and semaphore 1 could be defined as the indicator for the upper section of the memory. to take a resource, in this example the lower 2k of dual-port ram, the processor on the left port could write and then read a zero into semaphore 0. if this task were successfully completed (a zero was read back rather than a one), the left processor would assume control of the lower 2k. meanwhile, the right processor would attempt to perform the same function. since this processor was attempting to gain control of the resource after the left processor, it would read back a one in response to the zero it had attempted to write into semaphore 0. at this point, the software could choose to try and gain control of the second 2k section by writing, then reading a zero into semaphore 1. if it succeeded in gaining control, it would lock out the left side. once the left side was finished with its task, it would write a one to semaphore 0 and may then try to gain access to semaphore 1. if semaphore 1 was still occupied by the right side, the left side could undo its semaphore request and perform other tasks until it was able to write, then read a zero into semaphore 1. if the right processor performs a similar task with semaphore 0, this protocol would allow the two processors to swap 2k blocks of dual-port ram with each other. the blocks do not have to by any particular size and can even be variable, depending upon the complexity of the software using the semaphore flags. all eight semaphores could be used to divide the dual-port ram or other shared resources into eight parts. semaphores can even be assigned different meanings on different sides rather than being given a common meaning as was shown in the example above. semaphores are a useful form of arbitration in systems like disk interfaces where the cpu must be locked out of a section of memory during a transfer and the i/o device cannot tolerate any wait states. with the use of semaphores, once the two devices had determined which memory area was ?off limits? to the cpu, both the cpu and the i/o devices could access their assigned portions of memory continuously without any wait states. semaphores are also useful in applications where no memory ?wait? state is available on one or both sides. once a semaphore handshake has been performed, both processors can access their assigned ram segments at full speed. another application is in the area of complex data structures. in this case, block arbitration is very important. for this application one processor may be responsible for building and updating a data structure. the other processor then reads and interprets that data structure. if the interpreting processor reads an incomplete data structure, a major error condition may exist. therefore, some sort of arbitration must be used between the two different processors. the building processor arbitrates for the block, locks it and then is able to go in and update the data structure. when the update is completed, the data structure block is released. this allows the interpreting processor to come back and read the complete data structure, thereby guaranteeing a consistent data structure. figure 3. idt71342 semaphore logic
6.42 idt71342sa/la high-speed 4k x 8 dual-port static ram with semaphore industrial and commercial temperature ranges 14 ordering information 2721 drw 15 x x x x a 9 9 9 a a d evice type power speed package process/ temperature range blank i j pf 20 25 35 45 55 70 sa la 71342 commercial (0 cto+70 c) industrial (-40 cto+85 c) 52-pin plcc (j52-1) 64-pin tqfp (pn64-1) speed in nanoseconds standard power low power 32k (4k x 8-bit) dual-port ram w/ semaphore commercial only commercial & industrial commercial & industrial commercial only commercial & industrial commercial only , the idt logo is a registered trademark of integrated device technology, inc. datasheet document history 1/12/99: initiated datasheet document history converted to new format cosmetic and typographical corrections added additional notes to pin configurations 6/9/99: changed drawing format 10/1/99: added industrial temperature ranges and removed corresponding notes 11/10/99: replaced idt logo 12/22/99: page 1 made corrections to drawing 6/26/00: page 3 increased storage temperature parameters clarified t a parameter page 4 dc electrical parameters?changed wording from "open" to "disabled" changed 500mv to 0mv in notes 1/12/00: pages 1 and 2 moved "description" to page 2 and adjusted page layouts page 1 added "(la only)" to paragraph page 2 fixed j52 package description in notes page 8 replaced bottom table with correct 10b table 01/29/09: page 14 removed "idt" from orderable part number corporate headquarters for sales: for tech support: 6024 silver creek valley road 800-345-7015 or 408-284-8200 408-284-2794 san jose, ca 95138 fax: 408-284-2775 dualporthelp@idt.com www.idt.com

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