application note a very low cost and powerful solution for v.23 application : ts7514 AN349/0695 by o.leenhardt - r. girard summary page 1 introduction .................................... ................... 1 2 programmable mode ............................................... 3 2.1 with what to program? . . . . . . . . . . . . . . . . . . . . . . . . . ................... 3 2.2 how to program? . . . . . . . . . . . ....................................... 4 2.3 timing diagrams . . . . ............................. ................... 4 3 the ts7514 registers ............................................... 5 3.1 mode register : rprog . . . . . . ....................................... 5 3.2 d.t.m.f. register : rdtmf . . . ......................................... 5 3.3 transmit attenuation register : ratte . . . . . . . . . . . . . . . . . . . . . . ....... 5 3.4 line monitoring register : rwlo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.5 transmit filter register : rptf. . . . . . . . . . . . . . . . . . ................... 5 3.6 receive filter register : rprf. . . ................................... 6 3.7 detection level and hysteresis register : rhcd ................... 6 3.8 receive channel register : rprx . . . . . . ............................. 6 4 the 4/2 wire conversion : the hybrid ............................... 6 5 the d.t.m.f. dialing ................................................. 6 6 ring detection ..................................................... 6 7 tone transmission and detection .................................. 8 7.1 2100hz transmission . . . . . . . . . ....................................... 8 7.2 2100hz detection . . . . . . . . . . . . ....................................... 8 7.3 low frequency tone detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 8 line monitoring ................................. ................... 9 9 other features ................................. ................... 9 10 conclusion ..................................... ................... 9 1 - introduction the ts7514 is a single chip f.s.k. voiceband modem offering a real low cost powerful solution for all c.c.i.t.t. v.23 recommended standard ap- plications. indeed, ts7514 integrates many possibilities and functionalities by requiring only very few external components. its block diagram is shown figure 1. the ts7514 main features are : programmable modes : - modem 75/1200 or 1200/75 bps (full duplex on 2 wire line), - modem 75/75 or 1200/1200 bps (full duplex on 4 wire line), - d.t.m.f. dialing, - analog test loop, - tone detection (ring, dialing, ...) programmable functions : - transmit/receive levels, - receive filter gain, - hysteresis and detection levels, - line monitoring level, - signalling frequency (2982hz) level additional features : - integrated duplexer, - auxiliary analog signal transmission (voiceband), - automatic bias distortion adjustment, - tax rejection filter (12 and 16khz), - fixed compromise equalization, - standard low cost crystal (3.579mhz), - c.m.o.s. technology, - less than 100mw power dissipation, - 5v supplies, - 24 pin package. 1/9
ts7514 rdi rdo xtal out xtal in v+ agnd dgnd v- 5v 0v 0v -5v rwlo ratte serial input register and data control carrier level detector fsk demodulator time base mx mx internal clocks rxd zco mode g att rc mx corr scf scf g rc mx rao2 rai2 rao1 rai1 dcd mode rprog rhdl rprx rprf rdtmf data address mod/ dtmf mc/bc rts txd prd enp frequency generator scf corr scf mx rc mode mx buzzer att mx wlo ato analog loop rptf atxl a1 a2 4-bit bus AN349-01.eps figure 1 : detailed block diagram ts7514 application note 2/9
this application note describes some of the ts7514 most important features detailed before from a typical and simplified application scheme shown figure 2 (more information are given in the following sheets). +5v -5v 10 m f10 m f ++ external signal 560 w 18k w 12k w 100nf to loudspeaker amplifier 39k w 6.8k w 2.2 m f 270k w 1.5k w 1 m f ctp 120 w (670 90003) (*) l1/tph1 l2 trisil (tpa 270a 18) tph2 transfo. (emt l 162) 12pf 12pf 3.579mhz (ls04) 4.7k w +5v 2n2222 1n4148 c o n t r o l s extal u.a.r.t. m.c.u. (*) : regulation required in france only txd rxd prd rts mc/bc mod/dtmf enp dcd zco xtal out xtal in rdi rfo wlo rao2 rai2 ato rai1 rao1 v+ atxi gndd gnda v- t s 7 5 1 4 560 w 12k w 100nf 100nf AN349-02.eps figure 2 : typical application information 2 - programmable mode 2.1 - with what to program ? the ts7514 contains 8 control registers. the programming used is serial where data input is txd or prd and clock input rts. from now, it is important to point out that during programming, the rts (request to send) signal and the txd (transmit data) signal to be transmit- ted from the local terminal over the telephone line are internally safeguarded in order to not modify the transmission. - by using txd either to program or transmit data, only one signal has to be managed. in this case, you must take in care to program the ts7514 out of the transitions between two successive data bits and during a maximum duration equal to a obit timeo (833.3 m sec. in 1200 bps) to avoid trans- mission errors. - by using prd to program the ts7514 allows to use txdonly for data to be transmitted and avoids the preceeding cautions but requires the man- agement of these two signals. the choice will depend on the application (micro- controller used, number of i/o ports, ..) txd is selected by enp = o0o ; prd by enp = o1o. ts7514 application note 3/9
2.2 - how to program ? the programming is indirect via an 8 bit shift regis- ter, called input register, least significant bits first. the 4 m.s.b.'s of the input register are the address of the control register to program ; the 4 l.s.b.'s the data. the input register is selected by mod/dtmf = mc/bc = o0o. then, rts (request to send) and txd (transmit data) signals are internally safeguarded and the corresponding pins must be used as clock (rts) and data to be programmed (txd). the rts clock, active on the falling edge, shifts the programming data available on txd or prd. the transfer of programming data to the control register previously addressed is made by rising mod/dtmf or mc/bc. from now, the rts signal comes back to its pre- vious functioning mode : request to send. there are 2 cases of end of programming : - at the end of programming of all the control registers, excepted rdtmf, mod/dtmf rises to o1o while mc/bc indicates the channels used for transmission before programming (o0o for low channel transmission, o1o for high channel trans- mission). - at the end of programming of rdtmf register only, mc/bc rises to o1o while mod/dtmf and rts are o0o during all the time of d.t.m.f. signal programmed transmission. 2.3 - timing diagrams txd or prd rts mod/dtmf mc/bc d1 d7 AN349-03.ai figure 3 : programming without transmission txd rts mod/dtmf mc/bc d0 d7 data AN349-04.ai figure 4 : programming during transmission txd or prd rts mod/dtmf mc/bc d0 programming d7 transmission AN349-05.ai figure 5 : dtmf programming and transmission ts7514 application note 4/9
3 - the ts7514 registers we are going to describe now the most important points to know about these eight control registers. note : in the following, all the bits described are the data bits of the control registers (x = don't care). for additional informations on these registers, refer to the ts7514 corresponding data sheet. 3.1 - mode register : rprog this control register allows to choose the function- ing mode of the ts7514 : either two different or the same channels for transmit and receive. the most used mode (power-up initialization) is the receive channel programmed in the opposite way to the transmit channel controlled by mc/bc pin. in this case, bits 2 and 3 must be programmed to o0o. if bit 3 is programmed to o0o while bit 2 is pro- grammed to o1o, then transmit and receive chan- nels are the same (high channel if mc/bc is o1o, low channel if mc/bc is o0o). this last mode can be used for the full duplex on 4 wire line modem functioning or for the test with an external analog loop between transmit and receive sections (this last mode is not a loop 3 (see rprf register)). 3.2 - d.t.m.f. register : rdtmf this control register allows the d.t.m.f. dialing from the ts7514. bits 0 and 1 program the 4 low frequencies of the d.t.m.f. signal, bits 2 and 3 the 4 high frequencies. this register is not initialized at the power-up. the following table give the correspondance be- tween the digit to be dialed and the data to be programmed. digit d3 d2 d1 d0 frequency (hz) low high 0 1 2 3 4 5 6 7 8 9 a b c d * o 0 0 0 1 0 0 1 0 0 1 1 1 1 1 0 1 1 0 1 0 0 1 0 0 1 0 1 1 1 1 0 0 1 0 0 0 0 0 0 1 1 1 0 0 1 1 1 1 1 0 0 0 1 1 1 0 0 0 0 1 0 1 1 1 941 697 697 697 770 770 770 852 852 852 697 770 852 941 941 941 1336 1209 1336 1477 1209 1336 1477 1209 1336 1477 1633 1633 1633 1633 1209 1477 3.3 - transmit attenuation register : ratte this control register allows to program a transmit attenuation from 0 (0000) to 13db (1101), with 1db step. with such values, the analog transmit output level on ato pin varies from + 4 (0000) to 9dbm (1101). two programming values (1110 and 1111) allows an infinite attenuation. such attenuation is automatically programmed at the power-up initialization. so, a different attenu- ation will have to be programmed to transmit data (typically 0dbm (0100) on ato pin). 3.4 - line monitoring register : rwlo this control register allows : - to monitor the transmit signal from 10 (0000) to 40db (0011) with 10db step, - to monitor the receive signal from 0 (0100) to 30db (0111) with 10db step, - to send a square wave signalling frequency (2982hz) with a level comprised between 4 (1000) and 34dbm (1011). this register is initialized to 11xx (neither monitor- ing nor signalling transmission) at the power-up. if a receive signal monitoring is programmed, it is possible to monitor also simultaneously the trans- mit signal on account of the non infinite rejection ratio of the hybrid (typically 20db) and thanks to the ts7514 internal architecture (see figure 1), the receive signal monitoring being implemented be- fore the receive filter. 3.5 - transmit filter register : rptf this control register allows to transmit on ato pin one of the following signals : - normal (power-up initialization) modem or d.t.m.f. signals (0000), - external voiceband analog signal through : - smoothing filter and attenuator (0001), - low-pass filter and attenuator (0010), - band-pass filter and attenuator (0011), - low frequency only (0100) in d.t.m.f. mode, - high frequency only (1000) in d.t.m.f. mode. ts7514 application note 5/9
3.6 - receive filter register : rprf this control register allows to program different configurations for the receive filter : - receive filter gain of 0 (xx00), 6 (xx01) or 12db (xx10), - receive channel looped back on the transmit channel with a 35dbm level and a 0db gain (xx11) for analog test loop (loop 3), - receive filter bypassed (x1xx) or not (x0xx), - external connection (1xxx) via a 2.2 m f non-po- larized capacitor between rfo and rdi pins. the external connection (bit 3 programmed to o1o) with the capacitor is the most used mode to connect the receive filter output to the demodulator input. nevertheless, if an internal connectionis used, bit 3 has to be programmedto o0o and externalcapacitor and connection between rfo and rdi pins have to be suppressed. this register is initialized to x001 (receive filter enabled with 6db gain) at the power-up. 3.7 - detection level and hysteresis register : rhcd this register allows to control : - the loss carrier detection level between 41 (x000) and 27dbm (x111) with 2db step, - the hysteresis between carrier detect on and off : 2.5 (0xxx) or 3.25 (1xxx) db. be careful that the loss carrier detection level value (n2) is given related to the demodulator input (rdi). the on-line loss carrier detection level (nl) is obtained by substracting from n2 the receive filter and the hybrid gain values. in consequence, the on-line detection level is ob- tained by adding to nl the hysteresis value. this register is initialized to 0000 ( 41dbm for loss carrier detection level with a 2.5db hysteresis) at the power-up. 3.8 - receive channel register : rprx this control register allows to program different configurations for the receive channel : - to use a wide (for dataand tone detection)(xx0x) or a narrow (for data only) (xx1x) band filter for the receive low channel, - to suppress (xxx1) or not (xxx0) the carrier detection delays for a ofasto carrier detection (dcd digital signal following the receive carrier signal level variations). this register is initialized to xx00 (wide band filter and carrier detection delays) at the power-up. line 560 w 560 w 18k w 12k w rao1 rai1 ato rai2 rao2 AN349-06.eps figure 6 4 - the 4/2 wire conversion : the hybrid the ts7514 integrates two operational amplifiers. so, the hybrid implementation consists of selecting only 5 resistors in order to obtain the best adapta- tion and rejection possible. with 5 % resistors and a transformer 600 w /600 w respecting the local agreement conditions, the hy- brid so designed offersan ato/ra02 rejection ratio upper than 20 db. 5 - the d.t.m.f. dialing to dial a digit (0,..., 9, a, b, c, d, * ,#) in d.t.m.f. consists of programming the rdtmf control regis- ter like an other register but leaving, at the end of programming, the mod/dtmf and rts signals to o0o during all the time desired (in practise, the time of pressing key on a dialer). no external component is required for this dialing. 6 - ring detection thanks to zco output, it is possible to obtain in a digital way the analog zero crossing signal avail- able on the ra02 pin of the ts7514. then, by not totally insulating the modem from the telephone line (l1, l2) and bypassing the receive filter, zco can deliver the digital form of the ringing signal that may be then processed by the microcontroller. ts7514 application note 6/9
with the scheme given figure 7, we avoid to use opto-coupler and other externalassociatedcompo- nents to detect ring, the only external components required being a resistor and a capacitor. when the modem is connected to the telephone line (l1, l2), the components are bypassed (see relay) and the telephone set (tph1, tph2) discon- nected. the ringing signal (50hz alternative voltage super- imposed to the 50v telephone line voltage), is so attenuated by the resistor but the level is sufficient to be detected by the ts7514. do not forget during the detection to bypass the receive filter in the rprf register (bit 2 pro- grammed to o1o). so programmed, the ts7514 output on zco pin a 50hz digital signal and on dcd pin the ring oen- veloppeo (figure 8). dcd zco 15 ms 20 ms 1.5 s AN349-08.ai figure 8 modem rao1 rai1 cnt emt l 162 (e.m.t.) 1.5k w /3w 2.2 m f/63 v ctp 670 90003 (12 0 w ) (r.t.c.) 2n2222 1n4148 4.7k w 1 m f/63v 270k w tpa270a18 (sgs-thomson) l1 l2 tph1 tph2 regulation required in france only AN349-07.eps figure 7 ts7514 application note 7/9
7 - one transmission and detection 7.1 - 2100hz transmission (figure 9) to send the 2100hz answer tone over the tele- phone line, the ts7514 must be programmed as follows : - mod/dtmf = o1o (modem), - mc/bc = o1o (main channel), - txd = o0o (2100 hz), - rts = o0o (transmission). 7.2 - 2100hz detection (figure 10) to detect the 2100hz answer tone sended by the far-end modem, the ts7514 must be programmed as follows : - rts = o1o (no transmission), - mod/dtmf = o0o (tone detection), - mc/bc = o0o (back channel). so programmed, the ts7514 detects the 2100hz answer tone on line if dcd = o0o (carrier detection) and rxd = o0o (2100hz). 7.3 - low frequency tone detection (figure 11) to detect low frequency tones (typically the 440hz dialing tone in france) ; the ts7514 must be pro- grammed as follows : - rts = o1o (no transmission), - mod/dtmf = o0o (tone detection), - mc/bc = o1o (main channel), then, such tones are present on line if dcd = o0o (carrier detection). txd line rts mod/dtmf mc/bc AN349-09.ai figure 9 rxd line rts mod/dtmf mc/bc dcd AN349-10.ai figure 10 line rts mod/dtmf mc/bc dcd AN349-11.ai note : in this mode, the rprx register is automatically programmed to wide band filter for the receive low channel. figure 11 ts7514 application note 8/9
8 - line monitoring to monitor the different signals present on the telephone line, figures 12 and 13 give two typical loud-speaker amplifier application schemes. thanks to rwlo monitoring level programming register, no external potentiometer is required to adjust the volume. 9 - other features ? by atxi, it is possible to send a voiceband signal over the telephone line, ? the xtalout may be used to implement via a buffer, the external clock of the microcontroller, ? the lay-out implementation must be as clean as possible in order to obtain the best electrical performances : - separation between analog and digital parts and tracks of the board, - analog and digital grounds separated and con- nected in a single point, - a ground plane for the component side, - a star distributed power supplies (idem for ground) to avoid any possible loop, - a maximum capacitive uncoupling as close as possible to the device, - a connection as short as possible between rfo and rdi via the external capacitor. 10 - conclusion we just saw, with this application note, the different functions and internal possibilities included in the ts7514 among which d.t.m.f. dialing, integrated duplexer, tone and ring detection and transmit and receive channel programmings are the most inte- resting. for these features and all the others, only about 20 external passive components (resistors, capaci- tors, ...) are required (out of microcontroller inter- face) to implement a complete v.23 modem. the ts7514 is a real low cost and powerful solution for all c.c.i.t.t. v.23 recommended standard ap- plications. 1 2 3 4 5 6 7 8 loudspeaker (8 w ) +5v +5 v wlo (ts7514) 120 w 47 m f 1 w 47 m f 47 m f 100nf 100nf 470pf tba820m AN349-12.eps figure 12 1 2 3 4 58 loudspeaker (8 w ) +5v wlo (ts7514) tda7231 100 m f 100 m f 100nf 100nf 47 w 470 m f AN349-13.eps figure 13 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. ts7514 application note 9/9
|
