CALL ESTA8LISHMENT Elelo~e two modems can exchange data, an electrical connecoon thraugh the phon. system must be establ~shad. Although it may assist in call oststHishment, a rr~rJdem ty~cally does not play a malor role. A call may be originated manually or au(omalically and it may ba answered manually or automatcally. Manual Calling - Manual calling is pertormed t~y a person who dials the number. waits tor an answer, Ihen places the calling rnodern into data hansmission mode. Automatic Calling - Automalic calling i5 typ cally pertormr~d by an automatic calling unit [ACU) which generates the appropriate dialing pulse or dual-lone sequence required to call the remotr, (called) modem. The ACU also has the ability to detect an answer tone trom the called modem and place the calling morJem inlo data transmission mode. Manual Answering - Manual answering is pertormed by a person who hears tha phona ring, liKs tha receiver. causes the called modem to send an answer tone /o the calling mradem, and places ttie calied rnodam inlo dala transmission rnode. Autornabc Answering - Autornatic answering is pertorn~ed by a raltett rnor~rn with a data acress arrangement (DM). The DM detects a nngmg signal, takos the phone circuit ort-hook (COrrespOrKting to litting tha retedver) and ins~uots the called modem to commence tha auto-answer sequence. Next the called rnodern sands out silenca on the Fr~a, toFowed by an answer tone. When this tone is detected by the caHing modern, the connectic~ is considerod to hava been established. The Am79t0 provides assistance lo; automatic answering through the RING signal as tollows, Observe the upper right-hand portion ol Fi~ure B(a). Assurne that DATA TERMINAL READY (DTR) has recentty been asserted to cause exit Irom Ihe initial conditions. Note that i' DtR remains OFF, RING is ignored. Assurne also that RTS and EIRTS are OFF and that the mode control lir~es (MCO-MC4) sobct a norrnal rr~odem r,onfiguration, r~ot a loopback rnr~te. Automabc answering is inibated by recsipt ot a LOW tsvol at the RING input, causing errtranco to the auto- answer sequence dapicied in hgure B(c). The Arn7910 outpu~ silence (0.0 volts) at rts TRANSMITTED CARRIER (TC) output lor a bmo, tS'L, tdiowed by t,ho answer tono f® a time, tAT. The CARRIER DETECT (CD) pn is clemped OFF and ~e RECEIVED DATA (RD) signal is therelore clemper.t to a MARK (HIGH) during the autr~answer 6equence. Upon Compk~tK'n ot the answer tone, Z~ k releasod. 11 tho mode lines (NICaMC4) select a 202 or V.23 rnode, the transmit filters are set to tho forward channel anr.t the recsive hlters are set to the back channel duAng the auto answer sequence. At the end d the autr~answer sequence, rdum is made to poinl A in thc loop d tho upper right-hano portion ot Figura 8(a). Note tha s~ the answer llag has been set, tho auto-answer sequence cennot be entered agein unless ~i is first tumed OFF, ~en ON. At this point the phone Binc coru#ction has been established and dala transmission or recoption may begin. Tha RING input may be activated trorn a conditior~ed DAA Ring Indkator ou~put lor outomatic answeri~ it may be activated by a swilch tor manual answering. Tying RtNG HIGH will disable the auto-answer lunction ot the Am7910. DATA TRANSIlISSilON Foll Oupbs Folbwing call edablishrncnt, lull dupbx data transmission cen be ~ I startad by ei~ar the caBled or Caning rr~m. In other words, it the O |cor~c~ has b~n esta~ishad and ~o rnodem is hoping B~rough pdnt ~ h h~gure 8(a), it no br~r rnaRars whid~ is mO calied and which Is tbe calEng modem. Dala transmission Is initiated by assening REOUEST TO SEND (RTS), At th~s bmo tt~ TRANSMtTTED DATA (TO) inpu1 will be releasod and a mc~d- ulated carrier can appaar at tho TRANSMITTED CARRIER (TC) outpuh Following ~ delay. IRCON. CLEAR TO SEND (CTS) wii' turn ON. A! this tima. Cata may be transmitied through tho TO input It is a common protocol tor the user to alvvays present a MARK al the TD input before RTS is asserned and during the IRCON delay. Dala transmissioncontinues unbl RTS is tumed OFF Following a shon delay, tRCO`F'CTS tums OFF. As soon as RTS r~s OFF, the TD inpul i5 ignored ar~d the TC output i5 set to 0.0 volts (siler~ce). Aher CTS larns OFF, the state machine relums lo point A in F,~ure B(a). Halt Duplex When a hal1 doplex mode is selecied (202 or V.23l, dala trans- mission can be either on the main channel at 1200!600 baud or on Ihe back char~nel at 5175 baud. In normat halt dup~ex operation a single rnodem is either transmittrl9 on the main and receiving on the back channel or vico vr~rsa In the Am7910 control of tho transminer and receiver filters to tho proper channel is perlormed by RTS. When RTS is assened, the Iransminer hlters and syn- thesizer are sel to transmit on the main channet; the recedver lilters are set lo receive on the back channel. Therefore, whenever RTS is on, BRTS shouid not be asserted sir~ce the transmitter cenhol t~t usad for the back channel. When RTS is OFF and a haR doplex rnode is selected, the transrnittet fitters and synlhesizer are sel to the back channel the recelver itilters are set to the main charmel. It h~ anrJ ~iT3õ are asserted sirnuhane ously RTS wilt take precedence. Hov~ever, il BRTS is asserted bebre RTS and the back channed data transrnission sequence has been enlered (Fboure Et(b)). RTS will be ignored until BRTS is turned OFF. The state machine sequences ~r rnain and back diann61 trans- mission diHer slighHy and are rJepicied in Figure B" Assume the state machine is idling through point A in Fbure 8(a). hlain Channel This transmission seqwnc. is entered K a 202 or V.23 mode i5 selectad and RTS Is asseried. Since the recelver is no~r lorced to the back channel, the RECEIVED OATA {RD) signal is dampad to a MARK; and the CARRIER DETECT s~nal is damped OFF. The TRANSMITTED DATA input (TD) is raleased antt a carrier appears at Ihe TRANSMITTED CARRIER output whkh lollows the MARKISPACE applied to TD. RTS turning ON initiatos a delay, tRCoN. at the end of which the CLEAR TO SEND (CTS) output goss LOW. When CTS rgees LOW data may be transrnit- ted through inpul TD. Dala transmission contnues unbl RTS is turned OFF. At this time soveral evenis are indbsted. First a delay. t''COFF, iS initiated at the and ol which CTS turns OFF. The TD inpul is ignored as soon as ~ 9Oes OFF. 1' a 202 tnode is selected, a soft turn o~l tone appaars at ~ TC output lor a time. tSTo. lollowed by slilence (0.0 votts) For both 202 and V 23 rnodes a squekh peried, tSQ, is Wtiated when RTS r~s OFF. Durinrg this perrod the CD outpul is clemped OFF. torcliryt the RD outpult to a MARK c~ndition. The squelch perr,od begins as soon ús RTS goes OFF and thu5 owrtap5 both tRCOFF and ISTO- At the and o! the squelch peried, Iha stala machine retums to the idle bop at paint A in Figura 8(a). Tho raasons lor squskh and soK-turnol1 are as blbv~s: Soh Turn-OtI: Whan RTS is turned OFF st tt. emd oi a tnessago, transients occur which rnsg cause spunous sp*cc 5rgnals to bo retedvad at a remotei rsodem. Dunng soh turn~on the rnodem trans~nits a wh cairrier hequency lor a parliod, tSTo. alter ~S ie lurned OFF. Th~s resulls in a steady MARK on the RECLIVED DAtA (RD) l~ne ot the remote mr~tem Sr~uelch The iar al recckver musl be turned OFF sher RTS is OFF, unt~l Ihe slart ol ca~r~er detecl, so tbaN'ne Irans~enis are not dernodulated The proceSs ol disableng Ihe rece~ver aher RTS ~s turned OFF ~s called squelch,ng. 6tack Cnannel This transmission sequence, shown in F'gure Bib). is entered ii a 202 or V.23 rnode ~s selected, RTS rs OFF, and BRTS es asserted Tne BACK CARRIER DETECT (BCD) Oulpul is lorced OFF and the BACK RECEIVED DATA IBRD) oulpul is clamped to a MARK. The BACK TRANSMITTED DATA inpul (BTD) is úe- leased and a carrier appears at the TC outpul vvhich tollows the MARt<'SPACE eppleed to BTD. Tuming ON BRTS ~nihales a delay, tBRCoN at the end o'vvhich ~he BACK CLEAR TO SEND (B~) output goes LOW When ~S gnes LOW data may be Iransmitted through input BTD. Data Iransmission continues unt~l BRTS is turned OFF. The inpul BTD is immect,ateiy igno~ed and the TC output is silenced (set to 0.0 volts) Follovving a short delay, IgRcoFf. the outpul BGTS goes OFF. The signals BCD and BRD are released and the state machine retums to idle at paint A ot F'gure 8(a) In 202 back channel mode, BTD shouid t~e bed HIGH. Then EIRTS controls the ON OFF keying modolation When BRTS is LOW, 387Hz appears at the TC oulput, when BRTS is HIGH, 0 votts appaars at TC. DAtA RECEPTION Data receplion is conlrolled by state machir~e 2 and depicted in hgure 9. At power on the machine enters initial conditions and remains there until UtR is asserted. It then t~ops until either CARRiER DEfECT(CD) or BACK CARRiER DETECT (BCD) occurs. Full Duplex In tull duplex data receplion, CARRIER DETECT may appear út any time siter the phor~e conner,~;on has been established. fleception is independent d transmission. v,nwn the rec~iver rdetecLs a valid carrier tor at bast a bme, tCPON. tbe output CD is b~rnod ON, the RECEIVE[) DATA (RD) output is released. ar~d velid dala cen oe oblained al RD. Data is recsivad unGI the recsi'ver de ects bss ol carner lor at tea51 e time. ICDoFF. At Ihis (time the CD oulput is turned OFF and RD is dan~ped lo a MAR K. The state machir~e relurr~s to the idle bop al point E. 1 Hall Duplex As disoussed in d~e data Iransmission section above, when a hall duplex mode has been selecled, Ihe signal RTS conlrols whelher the main channel is transmitan9 or receiving Tne back channel can ooly do the opposite Irom the main. 11 RTS is OFF, then CARRIER DETECT may be asserted and the data recep- lion sequence is idenncal to that d~scussod above lor tull dup- lex reception. As lor~g as RTS remains OFF, BACK CARflIER DETEC:T ~'ill never be asserted. 11 RTS is ON, then CARRIER DElECT wili never be asserled. Inslead the receiver will look for a valid carner in the back channel frequency band. It a vatid carrier exisis lor at least a time, tgCDor4. the output BACK CARRIEn DETECT (BCD) is turned ON, the BACK RECEIVED DATA (BRD) outpul is released and valid dala cen be obtained at BRD. Dala is received unlil the receiver delecls loss o'back channel receivad signal lor al leasl 0me, tBCDOFF. At this time the BCD outpul is turned OFF. Dala outpul, BRD, is clarnped lo a MARK il a V.23 mode is selected. For 202 back channel m ode, BCD represents the reccived data. The BRD Outpul cen be ignored. The stale machine relurns to the idle loop at poinl E. LOOPaACK Ten modes exist to allow bolh analog and digilal loopback for each modem specification met by the Arn7910 When a loopback mode is selected, the signal processing (fillers, etc.) lor both the transmitter and recelver is set to process the same channel or frequency band. This allows the analog output, TRANSMITTED CARRIER, and the analog input, RECEIVED CARRIER. to be r;onnected lor local analog loopback. Aitematively the digital data signals, TD and RD or BTD and BnD. con be connected exter- nally, allowing a remole rnodem to test the Jocal mrt~m ~h hc digital dala signals looped back. When a loopback mode is selecied, Iha state machine sequences are allered sligh~t. Firsl, auto-answer is disabled. Serx~d. i1 a hatf duplex toopback mode is selecIed (202 or V.23), t~e bcal CARRIER DETECT/BCD is nol lorced OFF ~rhen RTsitaRTs is "ce~rt~ The 202 and V.23 main bopback modes anow use in a 4-wire configuration at 1200 bps e e~ _ ~"C ~ ~ ~ Äc - ~ _, ~ 1 -s