application note st75c502 - ram mapping AN539/0695 by william glass contents page i introduction . . . . . . . . . .......................... ................... 1 ii echo canceller (v.32bis only) . ....................................... 2 iii timing recovery . . . . . . . . . . ......................................... 2 iv carrier recovery . . . . . . . . ......................................... 2 v equalizer, agc . . ................................................... 2 vi handshake, retrain, rate negotiation . . . . . . . . . . . . . . . . . . . . . . ....... 4 vii carrier detect . . . . . . . . . . . . . . . . . . . . . . . ............................. 6 viii transmit filter coeficients . . . . . . . . . . ............................. 6 ix tone detector programming . . . . . . . . . . . . . . . . . . . ................... 7 x general purpose . . . . . . . . . . . ....................................... 8 xi tone generator ................................................... 8 xii default optionnal status . . . . . . . . . . . . ............................. 9 xiii ring . . . . . . . . . . ...................................................... 9 xiv adpcm. . . . . . . . . . . . . . . . . . . . . . . ....................... ................ 9 xv appendix . . . . . . . . . . . ............................. ................... 10 i - introduction the purpose of this application note is to explain what are the ointeresting internalvariableso 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 and internal peripherals can be ac- cessed using the three above mentioned com- mands. 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 2.0 of the st75c502. there is no guarantee that it will remain exactely the same for further revisions. 1/10
ii - echo canceller (v.32bis only) _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 (r) residual echo power estimator for determiningloss of connection.the abs() value of this variable will be greater than $20 to indicate connection loss, otherwise near 0. freqoff (r) far-end echo frequency offset. offset = freqoff x 0.0366 in hz typically, freqoff = $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 than -69dbm). iii - timing recovery frqofflt (r) receive clock frequency offset. psithrsh (r) 0.94 degree 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 = frqofflt psithrsh ? 0.94 360 the normal timing offset is within 10 -4 for most connections. iv - carrier recovery frqoff (r) receive carrier frequency offset. offset = frqoff x 0.0366 in hz. typically, frqoff = $1b(27) for 1hz. v - equalizer, agc _rx_sta (r/w) equalizer and agc can be frozen independentlyor simultaneously. bit 0 : freeze equalizer (the equalizer is frozen if this bit is 1). bit 2 : freeze agc (the agc is frozen if this bit is 1). _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 (r/w) automatic gain control level for receive signal varies from $80(0dbm) to $7fff (48dbm). st75c502 - ram mapping 2/10
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 30db 27db 24db 21db 18db 15db 12db staqua (r) a 16-bit number between 0 and 127 indicating the receive quality (also available in 8-bit status word byte 2, staqua in dual port ram). the following formula is implemented in dsp software : staqua = 127 - scaqua ? rdqua and is limited between 0 and 127. a value of 127 indicates a very good receive signal quality while 0 indicates a very poor signal quality. the coefficient scaqua is mode dependendentand was chosen to give a value for staqua of 63 when the receive snr is such that the expected bit error rate is 10e-5, that is, 1 error for every 100 000 bits received. refer to the following chartsfor expected values of staqua, ber on flat telephone line. 1e -3 1e -4 1e -5 1e -6 1e -7 1e -8 1e -9 0 316395127 1e -2 staqua ber AN539-01.eps figure 1 scaqua (r/w) the coefficient for calculing staqua above is automatically programmed according to the mode specified in the conf command and it is possible to overwrite its value at the end of the synchronization sequence if the user desires a different value for the quality indication. generally, reducing the value read by 1/2 will imply that an staqua value of 31 will correspond with a 10 -5 ber and doubling the value will imply that an staqua value of 127 will correspond with a 10 -5 ber in the above table. _sucth (r/w) a threshold value for staqua for determining the programming of pnsucs bit in hshk_pha word described below. the default value is programmed to 64 at the execution of a conf command and can be modified there after. _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 equalizer coefficients. st75c502 - ram mapping 3/10
vi - handshake, retrain, rate negotiation _sspeed (r) negociated speed. this 8-bit number is available in staop0 in modem mode (refer to data sheet for values). _stav54e (r) this 8-bit number is available in staop1 in modem mode and indicates status v.54 and v.22bis test logs (refer to data sheet for values). hshk_pha (r) handshake progression counter contains information about the progress of the handshake in v.32 and v.22bis modes. this 8-bit value is available in staop2 in modem mode. it can be read to examine the progression of the handshake and it contains normal values and error values as below : autobaud orig mode event hshk_pha value wait answer tone wait end answer tone no autobaud and waiting usc1 autobaud waiting ac or usc1 $01 $02 $03 $04 autobaud answ mode event hshk_pha value waiting hsk command generating answer tone generating silence $10 $11 $12 v.32 orig mode event hshk_pha normal value hshk_pha 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 hshk_pha normal value hshk_pha 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 $50 $8 for rtrn, $9 for rrn $1 $2 $3 $4 $5 $6, $a no r det after rrn $7 v.22bis orig mode event hshk_pha normal value hshk usc1_det scr1_det s1_det data_mode $60 $61 $62 $63 $70 st75c502 - ram mapping 4/10
v.22bis answ mode event hshk_pha normal value hshk scr1_det s1_det data_mode $80 $82 $83 $90 fax mode while transmiting p1s p2s pns prs scr1s = %00000001 generate echo protection tone = %00000010 generate phase reversals = %00000100 generate training sequence = %00001000 generate rate sequence = %00010000 generate scrambled one's while receiving p2s pndets pns prdets pnsucs scr1s = %00000010 detect phase reversals = %00100000 detect training sequence (latched) = %00000100 detect training sequence = %01000000 detect rate sequence (latched) = %10000000 equalizer trainning succes (latched) = %00010000 detect scrambled one's note that prs and prdet are only valid in v.17 and v.33 modes. _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. _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 : (itu-t 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. st75c502 - ram mapping 5/10
_curmod (r/w) to give the final negotiatedmode for autobaudapplications(especiallyusefulfor fsk) or data mode configuration. d7 d6 d5 d4 d3 d2 d1 d0 ccitt qammd tcmmd fdumd lowmd eccmd not used ansmd ccitt : 1 : ccitt modes. 0 : bell modes. qammd : 1 : qam v.32bis, v.32, v.22bis, v.22, b212a, v.17, v.33, v.29, v.27. 0 : v.21, v.23, b103 fsk modes. tcdmmd: 1 : trellis mode (v.17, v.33 or v.32(bis)). 0 : non-trellis mode. fdumd : 1 : full duplex mode such as v.32(bis), v.22(bis), b212a, v.21, v.23, b103. 0 : half duplex modes (fax) v.21ch2, v.17, v.33, v.29, v.27. lowmd : 1 : v.27 or v.32 or v.22 or v.21 or b103. 0 : v.29 or v.32bis or v.22b or v.23. eccmd : 1 : echo canceller mode v.32(bis). 0 : no echo canceller mode (others). ansmd : 1 : answer mode. 0 : originate mode. vii - carrier detect deth1 deth lossth1 lossth (r/w) (r/w) (r/w) (r/w) fast detection threshold. 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 enhancedprecision. there are four thresholds programmed with default values for each of the modes v.22bis, 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 threshold 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) viii - 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 conjonction with gain for fine adjustment of the transmit signal. up and down scaling. st75c502 - ram mapping 6/10
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 externalmemory, 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) ix - tone detector programming levout (r/w) 16 programmable static levels. biqcoef (r/w) 16*2*6 biquad 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)] st75c502 - ram mapping 7/10
cpwire (r/w) 16 comparator input wiring addresses. format = [comparator+(msb),comparator-(lsb)] the wiring addresses furnished in bpwire,cpwire are from the following possible 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 o1o the signal at the positive input of the comparator is higher than that at the negative input. only _ntdcell bits are valid at one time, the other one are 0. tonedet0 tonedet1 d0 call wait bpf 440hz d0 an1300 bpf d1 rxsig < -21dbm d1 org : an1300 > az1800 ans : an1300 > oz2100 d2 cplow lpf 650hz d2 an1650 bpf d3 cphigh hpf 600hz d3 org : an1650 > az1800 ans : an1650 > oz2100 d4 cphigh < cplow d4 org : ans2100 bpf ans : org1800 bpf d5 org: az1800 notch ans: oz2100 notch d5 org : ans2100 > az1800 ans : org1800 > oz2100 d6 an600 bpf 600hz d6 ans2225 bpf d7 org : an600 > az1800 ans : an600 > oz2100 d7 org : ans2225 > az1800 ans : ans2225 > oz2100 x - general purpose _txgain (r/w) transmit gain. any signal to transmit is multiplied by this number. this is the value modified by setgn command. xi - 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). st75c502 - ram mapping 8/10
xii - default optional status uaddr (r/w) size 3 : address of the dsp's variable regulary displayed into the optionnal status word. these address can be modified with the dosr command. xiii - ring rng_fmin (r/w) the default value for this variable is 35. a ring signal of 68hz is periodic every 35 bauds at 2400hz. rng_fmax (r/w) the default value for this variable is 160. a ring signal of 15hz is periodic every 160 bauds at 2400hz. ring_period (r) output of the ring detector. this word is identiqual to the staop2 byte when in tone mode (neither dtmf receiver neither modem mode). the content of that word is the duration of the ring period. the formula to compute the ring frequency is : ring_frequency = 2400 ring_period in hz. 200ms ring sta_ring ring_period 0 t1 t2 t3 t4 0 t'1 t'2 t'3 AN539-02.eps figure 2 xiv - adpcm noise (r/w) the default value is $c after conf command and can be modified to increase or decrease the background noise level in the voice activity detection algorithm. the value is complemented at the sample rate giving a periodic signal at 3600hz. transmax (r/w) the default value is 90 after conf command and represents, in each frame of 30ms, the maximum number of transitions or zero-crossings to keep the voice activity detector active. the internal signal, voice, represents the output of this detector and is updated every 30ms. cntmax (r/w) the default value is 14400 (2s) after conf command and represents the preload value for a counter. the counter is update at the sample rate of 7200hz. it is either preloaded if voice (from above) is active or decremented if voice is inactive. if the counteris not 0, carrier detect is raised. effectively, the user can increase (decrease) the duration of carrier detect after loss of a voice signal by increasing (decreasing) the value of cntmax. prgthrsh (r/w) the voice activity detector has an absolute signal level threshold in parallel with the zero-crossing detector described above. the default value of prgthrsh is 0 after the conf command and designates the threshold to be the average level measured during the previous detection of voice activity by the zero-crossing method. if prgthrsh is changed by the user to a non-zero value, the actual value programmed is the threshold for the detector. thus, the absolute signal detector can be disabled by programming a large value such as $7fff for prgthrsh. st75c502 - ram mapping 9/10
xv - appendix : address equivalences for version 1.0 and 1.2 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 microelectronics. specifications mentioned in this publication are subject to change without noti ce. this publication supersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of sgs-thomson microelectronics. ? 1995 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 confo rms to the i 2 c standard specifications as defined by philips. sgs-thomson microelectronics group of companies australia - brazil - china - france - germany - hong kong - italy - japan - korea - malaysia - malta - morocco the netherlands - singapore - spain - sweden - switzerland - taiwan - thailand - united kingdom - u.s.a. variable address echo canceller _rtdelay $1016 _ec_sta $1019 pwrest $1bad freoff $1bb1 delta $1bbd feecenbl $1bce timing recovery frqofft $1e8c psithrsh $1e97 carrier recovery frqoff $1ea3 equalizer,agc _rx_sta $1017 _agcsca $1193 rdqua $12a7 _rdcpt $1048 eqfrk0e $1cbc eqfrk1e $1cfc staqua $1058 scaqua $12a6 _sucth $1fce handshake,retrain, rate negotiati on hshk_pha $11bb _re_hsk $11bd _tspeed $11af _trword $11b0 _rword $1014 rnthrsh $12aa _curmod $1011 _sspeed $11ba _stav54e $11a1 carrier detect deth1 $1f9a deth $1f99 lossth1 $1f9c lossth $1f9b variable address transmit filter coeficients txcoef $12e4 gain $12e2 shiftval $12e1 tone detector programming levout $13e6 biqcoef $1476 powcoef $1536 bpwire $1456 cpwire $1466 _ntdcell $1006 _tonedet $1007 general purpose _txgain $1001 tone generator _tgnflg $1002 _tg0phc $1003 _tgnblk $13a8 default optionnal status uaddr $1e6e _tonedet $1007 dtmf_digit $174a neg_mode $11ba hshk_pha $11bb sta_loop $11a1 ring_period $1dd8 ring rng_fmax $1ddc rng_fmin $1ddb ring_period $1dda adpcm noise $1595 transmax $1596 cntmax $1599 prgthrsh $159f st75c502 - ram mapping 10/10
|
