application note ram mapping st75c50 AN536/0694 contents page 1 introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 echo canceller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 timing recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4 carrier recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 5 equalizer, agc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 handshake,retrain,rate negotiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 7 carrier detect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 8 transmit filter coeficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 9 tone detector programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 10 general purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 11 tone generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 12 appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1 - introduction the purpose of this application note is to explain what are the "interesting internal variables" that can be read, written or modified using the mr , mw , cr commands. some of these variables have dedicated com- mands to modify them, like setgn for _txgain or tone detector. however the whole ram (even external when using the st18933) and also the dual ram et internal peripherals can be accessed using the three above mentioned commands. the address, characteristic (r = read, w = write, r/w = read or write), and function of key data pump variables is listed below by basic modem functional blocks. caution : the mapping of the variables, given in the appendix is only valid for revision 1.0 of the st75c50. there is no guarantee that it will remain exactely the same for further revisions. 1/7
2 - echo canceller _rtdelay (r) round trip delay in number of bauds _ec_sta (r/w) echo canceller execution status word. the echo canceller can be frozen in data mode by reading _ec_sta and performing a logical or with the value $0002 before writing to _ec_sta. (i.e. other bits must not be changed) (pwrest+1) (r) residual echo power estimator for determ ining loss of connection. the abs() value of this variable will be greater than $20 to indicate connection loss, otherwise near 0. (freqoff+3) (r) far-end echo frequency offset. offset = frqoff*.0366 in hz typically, frqoff = $1b(27) for 1hz. delta (r) initial far-end echo power after near end echo canceller convergance. this variable can be read in data mode and has the following typical values. value power $fff6 $fff7 . $0000 . $000a (-10) (- 9) . (0) . (+10) - 9dbm -12dbm . -39dbm . -69dbm feecenbl (r) far end echo canceller is enabled. $ffff = enabled $0000 = disabled (when initial far-end power is less han -69dbm. 3 - timing recovery (frqoff+1) (r) receive clock frequency offset. psithrsh (r) .94 deg timing phase adjustement threshold for timing signal dpll. comments : the local-to-remote modem timing offset can be calculated using the following formula : timing offset = frqoff psithrsh * .94 360 the normal timing offset is within +/- 1.0e-4 for most connections 4 - carrier recovery (frqoff+1) (r) receive carrier frequency offset. offset = frqoff*.0366 in hz. typically, frq off = $1b(27) for 1hz. 5 - equalizer, agc _rx_sta (r/w) equalizer and agc can be frozen independently or simultaneously. %-------- x - : : ........ x : .........1 = freeze equalizer .........1 = freeze agc - = do not change _rx_sta must be modified in data mode and the other bits must be unchanged. read the value and change only the corresponding bits in the _rx_sta word. (_agcsca+1) (r/w) automatic gain control level for receive signal varies from $80(0dbm) to $7fff (48dbm). ram mapping st75c50 application note 2/7
rdqua (r) equalizer error energy gives an idea of signal to noise ratio seen by the receiver. rdqua has the following typical values. value power $00c0 $0180 $0300 $0600 $0c00 $1800 $3000 30 db 27 db 24 db 21 db 18 db 15 db 12 db _rdcpt ( r ) output of demodulator. complex number, can be used to display the received eye. eqfrk0e (r/w) 32 complex even equalizer coefficients. eqfrk1e (r/w) 32 complex odd eq ualizer coefficients. 6 - handshake,retrain,rate negotiation _shsk (r) handshake progression counter contains information about the progress of the handshake in v.32 and v.22b modes. it can be read to examine the progression of the handshake and it contains normal values and error values as below: v.32 orig mode event shsk normal value shsk error value ac_det ac/ca det ca/ac det no ac det s_det sb_det r1_det s_det sb_det r3_det e_det data mode $20 $21 $22 $23 $24 $25 $26 $27 $28 $29 $2a $30 $1 $2 $b for rtrn, $c for rrn $4 $5 $6 $7 $8 $9, $d no r5 det after rrn $a v.32 answ mode event shsk normal value shsk error value aa_det aa/cc det no cc det s_det s_det2 sb_det r2_det e_det data mode $40 $41 $42 $43 $44 $45 $46 $47 $8 for rtrn, $9 for rrn $1 $2 $3 $4 $5 $6, $a no r det after rrn $7 v.22b mode event shsk normal value hsk data $60 orig,$80 answ $70 orig,$90 answ _re_hsk (r) stored r and e word values which were sent and received in their chronological order during the handshake, retrain, or rate negotiation. positions _re_hsk to (_re_hsk+4) contain history during handshake or retrain while (_re_hsk+5) to (_re_hsk+8) contain history during a rate negotiation request. ram mapping st75c50 application note 3/7
_tspeed (r/w) target speed initialized by conf or rtra commands but can be changed in data mode for the case of a remote rtra or rrn requests. %0000000000000010 %0000000000000011 %0000000000000100 %0000000000000101 %0000000000000110 %0000000000000111 %0000000000001000 = = = = = = = 1200 bps 2400 bps 4800 bps 7200 bps 9600 bps 12000 bps 14400 bps _trword _rword (r/w) target rword initialized by conf or rtra commands but can be changed (both of them) in data mode for the case of remote rtra or rrn requests. in reference to the ccitt recommendation the bits are programmed in the following order : (ccitt recommendation) b00, b01, b02, b03, b04, b05, b06, b07, b08, b09, b10, b11, b12, b13, b14, b15 ................ d15, d14, d13, d12, d11, d10, d09, d08, d07, d06, d05, d04, d03, d02, d01, d00 (_trword) rnthrsh (r/w) threshold for rate negotiation during handshake or retrain. the quality of the receive signal is observed (can be disabled by the command modc) and the corresponding r word is proposed in the handshake or retrain rate negotiation. the default value is $300. this gives the typical r word authorization characteristics as shown below: speed authorized snr 14400 12000 9600 7200 > 24db < 24db < 21db < 18db doubling the threshold will decrease the corresponding snr by 3db approximately. 7 - carrier detect deth1 deth lossth1 lossth (r/w) (r/w) (r/w) (r/w) fast detection thres hold slow detection threshold slow loss threshold fast loss threshold the carrier detect contains 2 signal level integrators, a fast integrator for quick detection with a limited precision and a slow integrator for enhanced precision. there are four thresholds programmed with default values for each of the modes v.22b, v.33, v.17, fsk, v.29, and v.27 which can be modified by the user after the conf command. typical values are shown below and doubling the value will increase the thres hold by approximately 6db : (-40dbm) (-44dbm) (-47dbm) (-51dbm) $b0 $90 $60 $40 deth1 (fast detection threshold) deth (slow detectiion threshold) lossth1 (slow loss threshold) lossth (fast loss threshold) ram mapping st75c50 application note 4/7
8 - transmit filter coeficients txcoef (r/w) address of first pulse shaping/compromise equalizer complex coefficient (16-bit real,16-bit imag). gain (r/w) attenuation factor for the transmit filter. shiftval (r/w) gain (left shift value) from 0 to 15. to be use in co njonction with gain for fine adjustment of the trans mit signal. up and down scaling. the pass-band pulse shaping and transmit compromise equalizer functions are combined in the transmit filter coeficients. the pulse shaping also performs the multi-phase interpolation from different baud rates to a fixed sample rate 7200hz (14400hz for v.27 4800) thus requiring multiple coeficient sub-tables containing complex (16-bit real,16-bit imag) coeficients. the number of coeficients depends on the shape, baud rate,and sampling rate. a default table depending on the compromise equalizer selected in the conf command is loaded from coeficient memory to external memory, after which, if desired, they can be modified by the user. the table below summarizes the location and the number of coeficients to be loaded. (* = default values) mode baud rate phase coef/phs strt adr roll-off* no. of compeq* v.32/33/17 2400 0 1 2 32 txcoef (txcoef+64) (txcoef+128) 0.125 3 v.29 2400 0 1 2 24 txcoef (txcoef+48) (txcoef+96) 0.20 2 v.27(2400) 1200 0 1 2 3 4 5 8 txcoef (txcoef+16) (txcoef+32) (txcoef+48) (txcoef+64) (txcoef+80) 0.50 1(flat) v.27(4800) 1600 0 1 2 3 4 5 6 7 8 7 txcoef (txcoef+14) (txcoef+28) (txcoef+42) (txcoef+56) (txcoef+70) (txcoef+84) (txcoef+98) (txcoef+112) 0.50 1(flat) v.22 orig/ans 600 0 1 2 3 4 5 6 7 8 9 10 11 5 txcoef (txcoef+10) (txcoef+20) (txcoef+30) (txcoef+40) (txcoef+50) (txcoef+60) (txcoef+70) (txcoef+80) (txcoef+90) (txcoef+100) (txcoef+110) 0.50 1(flat) ram mapping st75c50 application note 5/7
9 - tone detector programming levout (r/w) 16 programmable static levels. biqcoef (r/w) 16*2*6 b iquad coeficients. coef. order for each of 16 4th order cells : c0, c1, c2, c3, c4, c5, c6, c7, c8, c9, ca, cb where each 4th order cell has the following xfer function : out in = c0 c5 z 2 + 2 c3 z + 2 c4 z 2 - 2 c1 z - 2 z c6 cb z 2 + 2 c9 z + 2 ca z 2 - 2 c7 z - 2 c8 powcoef (r/w) 16 power coeficients p1 power estimator using absolute value of the input signal : out in = p1 1 z - ( 1 - p1 ) bpwire (r/w) 16 biquad and pwr estimator input wiring addresses format = [4th order biq(msb),pwr(lsb)] cpwire (r/w) 16 comparator input wiring addresses format = [comparator+(msb),comparator-(lsb)] the wiring addresses furnished in bpwire,cpwire are from the following poss ible sources : gnd rx signal rx signal*2 rx signal*4 4th order biq block output power output static levels programmed in levout $00 $01 $02 $03 $10 to $1f $20 to $2f $30 to $3f _ntdcell (r/w) number of tone detector cells active (0-15) _tonedet (r) outputs of tone detectors. the low byte of _tonedet contains the outputs of tone detector cells 0 to 8. the low byte of _tonedet+1 contains outputs of cells 9 to 15. when the corresponding bit is "1" the signal at the positive input of the comparator is higher than that at the negative input. only _ntdcell bits are v alid at one time, the other one are 0. 10 - general purpose _txgain (r/w) transmit gain. any signal to transmit is multiplied by this number. this is the v alue modified by setgn command. 11. tone generator _tgnflg (r/w) tone generator flag. each of the four low bits of this variable define if the corresponding tone generator is enabled. this is the value modified by a tgen command. _tg0phc (r/w) tone generator #0 phase reversal threshold. if different from 0, a phase reversal will be executed on the tone genarator #0 after _tg0phc bauds. this is used in v.32 answer tone generation (default value is 1080 for 450ms). _tgnblk (r/w) for each of the four tone generators (i) contains: _tgnblk+(3*i): frequence of tone (i.e. $4000 = 1800hz). _tgnblk+1+(3*i): instantanous phase. _tgnblk+2+(3*i): amplitude ($7fff refers to maximum signal). ram mapping st75c50 application note 6/7
12 - appendix address equivalences for version 1.0 variable address echo canceller _rtdelay $016 _ec_sta $019 pwrest $bac freqoff $bae delta $bbd feecenbl $bce timing recovery frqoff $e8a psithrsh $e95 carrier recovery frqoff $ea2 equalizer,agc _rx_sta $017 _agcsca $192 rdqua $2a7 _rdcpt $048 eqfrk0e $cbc eqfrk1e $cfc handshake,retrain, rate negotiation _shsk $1bb _re_hsk $1bd _tspeed $1af _trword $1b0 _rword $014 rnthrsh $2aa variable address carrier detect deth1 $f9a deth $f99 lossth1 $f9c lossth $f9b transmit filter coeficients txcoef $2e4 gain $2e2 shiftval $2e1 tone detector programming levout $3e6 biqcoef $476 powcoef $536 bpwire $456 cpwire $466 _ntdcell $006 _tonedet $007 general purpose _txgain $001 tone generator _tgnflg $002 _tg0phc $003 _tgnblk $3a8 caution add $1000 to the addresses when using st75c50 single chip or st75c50cia kit part. add $9000 to the addresses when using emulation module. information furnished is believed to be accurate and reliable. however, sgs-thomson microelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no licence is granted by implication or otherwise under any patent or patent rights of sgs-thomson microelectroni cs. specifications mentioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in lif e support devices or systems without express written approval of sgs-thomson microelectronics. ? 1994 sgs-thomson microelectronics - all rights reserved purchase of i 2 c components of sgs-thomson microelectronics, conveys a license under the philips i 2 c patent. rights to use these components in a i 2 c system, is granted provided that the system conforms to the i 2 c standard specifications as defined by philips. sgs-thomson microelectronics group of companies australia - brazil - china - france - germany - hong kong - i taly - japan - korea - malaysia - malta - morocco the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. ram mapping st75c50 application note 7/7
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