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Interrupted!LDU=UU@UUU>ULLV rJILULLVU=Ui?U?UI,LV *, } *SLFV?U0L5V9?UL5V?U *SL:V- *S?U *>ULU *S SLqV SU N`LV TLV S SLVNo connect }ion made!V N`LV rJILV S S JU/ N`LUVCLc c>CL+d b }ccc)ccI cILccLHdL+dcI cILd4C`L+d7CL+dcIL d c>CL+dc Scc #WFCI GC }ILEdLHdLccILdFCccILjdcLd *cc̓cLdc #WcLud Sc`LddJCI KCIL2e4C }QCPC I4CɀLd`PCiQCiQCPC ,8VCVCWCWC8LCLCMCMCPCiTCQCiUCKCJC7C }LfedI LLedLWed Sdd Lfe`TCUCdTCUCJCKC`Le SUCWCTCVCKCMCJCLCOCSC }NCRCFC GCLf8FCFCGCGCeFCee͌eLfRCSC dL f4C`RCSCeLe S`L(f#f }#fL)g Ub$f$fILOfLbLsf$fILff6C`Lsf$fILsfLvfL7fC %R S4C } *C V*4CLiLb S UbiiiI iILiLbLiiI iILiLiLi *SLi. *M c6C6Cɀ }LjLb hL*jLb6CL5jL8jLji iLfj *S UbIL`j. *LfjiL=j N`LnjACIL~j ._LjACILj `Lj5C } ?CKCJCBCHjjȌH ~SACILj /gLjACILj ijjH ~S JAC * *`Connection lost! S S`Lk jk S }k` S S S S SL!k S`" NL`k!Save configuration to diskٯ? k> * 0KIYLk *4CC } V*4CɀLk4C ILk4C򅣠G I4CɀLk4C I * ?J` receive: send: capture: upload: kkk }klFile to  ext or inary ? Press START to begin transferLMll" Nl *l m l*(m l * }CC L ?JC OCLl`lLl Nl * 0KllITLl7CLllIBLl7CLl`l, NllA }C`Lm m m m m m m)m m)LNmȌ mLQm mmmgmgmmLmm m m*(m m } * mLm *mL\mm m m*(m m DKD| *` ?JHi JHH m@C` Press any key }to cont,to endLnm@CmsDmwD ?JH J4C *Du V*4CɀLun4C ILUoC }Jm mL ommLn *mCLnLnmLn *CI CI*LnC *CHH *LnC *mI Ln } *LoL omLn JL,om VN JLOoLLom VN JIILLoLOoLznLUoL$n *`Lfoao`o`oao }i`oaoboGboLoLoLog-on sequence incorrect!o Nhh j`LoHmboHi`Lo ?J ?J }SoCoMG rJILpLqL"po coooI|Lmpo cooCLLpoC MoI|L,pCC AULjpLqLqo }I[Lqo coooIWLCqo coooI^Lpo co)oo co NLp Waiting for: p *o * } 3Tooo)o)LqL@qL=qo)o)MoIL=qL@qLpLqoIPL~qLaq Pausing...qU VN }o co WJLqo cooo coo *SLqoI^Lqo cooo) *SLqo *S ?JLo j`Lqq(qL }q *qLq` ?J ?JL?J"Waiting for call.to abort.L)rr VN S S S S rJIL\rU/ N k`Lrr SL }rrU N`L>rdit or o log-on ? Dial: dit or ial ? 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NLL, k R))80C1C8HCIC zLq  ^ *ICHC + *H }CC {LLCCMHL z LLHHINII1COC0CNC0CiPC1CiQC ʎDʆ EC DC }  4C *C V*4CɀLEG +HLV򅣠G I *L+`CiQC ʎDʆ EC DC a  L( <' $BROPHȌP #hP BO #QBRO # %B T} `T ' '  '`l' 8$ $B`*) LQ )B $ %YR #, %B ` 8$B} y%QR # %BҠ` 8$RQYɛ&Q`@BJRY 8AQE E`q!iJ!iK}QlJB)`BJʭC)0 4RɛC)@ `  ) }`RC) % %) R }R [$ I$? xIR %IP %X` 8$B)`BJLQX [$ I$xGF'R %GXCJJ)#R %}) ! EE %C)0 R` %  }L`BJ)@L!LQ`,l'HҥҩOh@ؘHF} E E ҙ' !%Fҍ I) EEhh@ؘH %L !H %H)ؘHPPD)>DL !}HDID)D)DКKejʻ LLL"Ll#L #L"L"L!L!LQ`QJiJK`)pRC) RCL!}L!)RC) RCL!п!"`D)E)E` #)D` #` #  # #)L" #  #)L" }# @ #)L" #D д #D)>L"D)L"D И #`B)`) Bx $ ҅X % #ݭB B # %B }B`B B #B B %"#`D LO$B B #L$P`) Q %`RSD)!  $ %PR} #SRL%# %L%#R R  #D LLQRSD) OR #L# #SRD DL!P y%)5ӅB}PxIR %IX y%2$3$ \% [#$$P0NBQP=ӭB) B)BD8`MD`B=ӭB)BD`<E})EM`,D`MQ`O`MOQB)B=өB`x $DQ% ҅X` !!>!X!-2 p2 }ҍ ҩxҢ ҍ` $ '$%$ '$ ӭ'' `x''' !}')ө%ҢX`s&%'x \NX`N`x %X [$` ` \% [$N`JJ`R"})R`Ș@``ҍҍҍҍҍT%&R%&8)H) =&X>&YhJ)5&Z6&[x C& &(@` #} a'+0_]U,T &JJJJ &\W,V &) &m\m')<]0 ^ JJ ^_'آT}XTU}YU$}]I]0_Ж`' ԘJJJJ  ԍҘ)  ԍ&'`)&@&`I`!!222BCCSSTdddtuu%}ɢ ?Ji'JJJJ)]&)]&&`"33DEUffwwr ATARI[R] XM301 MODEM[TM] TECHNICAL SOFTWARE SPECIFICATIONSThis manual contains the referencespecifications for th'}e softwareinterfaces used by applicationsprograms and the Operating System tocontrol the XM301 Modem. Cont(}entsSection 1: Description of the XM301Modem Interface With Other Products Family of Products Reference Documents)}Section 2: Logical Requirements forthe XM301 Modem Man/Machine Interface The Six Standard Input/OutputCommand Interf*}aces OPEN CLOSE INPUT OUTPUT STATUS Parameters Passed as Data Strings Error Handling Buffer+} Use Handler/Operating System Interface SECTION 1 DESCRIPTION OF THE XM301 MODEMThe XM301 Modem is a,} stand-aloneperipheral which connects to theATARI 400[TM]/800[TM], and theXL[TM]/XE[TM] series with the SIOinterface by m-}eans of the serial bus.The modem connects to the telephoneline by means of the RJ-11C jack.The modem control software re.}sides inthe internal ROM of the 8048 singlechip microprocessor. A separatesoftware handler will be disk-based.Interfac/}e With Other ProductsThe XM301 Modem is an input-outputperipheral, and performs no actionswithout instructions from ana0}pplications program. To use the XM301 Modem from ahigh-level language, the followingtypes of commands are required: 1} OPEN CLOSE GET (or equivalent READ, INPUT) PUT (or equivalent PRINT, WRITE) POKE PEEKFamily Of Produ2}ctsThe XM301 Modem performstelecommunications functions inconjunction with applicationsdesigned specifically for use wi3}ththe XM301. It is interfacecompatible with the Telelink II[TM]application. The modem is capable ofaccepting any comman4}ds issued by theTelelink II handler withoutperforming in an irregular fashion orreturning the "illegal command" errorcode5}.Reference DocumentsATARI Home Computer System TechnicalReference Notes: Operating System User's Manual Operating 6}System Source Listing andHardware ManualThe Technical Reference Notes areavailable from ATARI CustomerRelations, P.O. B7}ox 61657, Sunnyvale,CA 94088. Cost: $29.95 plus $2.50for shipping. California residentsshould add appropriate sales ta8}x.Write "Order for Technical ReferenceNotes" on the outside of the envelopeto speed up the order process. 9}SECTION 2 LOGICAL REQUIREMENTS FOR THE XM301MODEMThe handler is provided by anAUTORUN.SYS disk file.The modem contro:}ller, an 8048Hmicroprocessor, is accessed by thehandler through the serial I/Ochannel.The handler uses RAM for input an;}doutput buffers, variables forcommunicating with the user, andinternal variables. Internalvariables are in low memory, w<}ith onevariable (CMCMD) permanentlyallocated in the Operating Systemdatabase for use by this handler.User communication=} variables are thesystem IOCBs, the zero page IOCB, andthe command flag CMCMD. IOCB use isdescribed in the ATARI Home Com>}puterSystem Technical Reference Notes, andin Section 2, Handler/OperatingSystem Interface. CMCMD use isdescribed in Sect?}ion 2, ParametersPassed As Data Strings.The XM301 handler allocates an inputand output buffer where data can beentered @}between the application andthe handler. The output is 64 byteslong; the input buffer is 256 byteslong. There are 2 bytesA} used forbuffer control variables by thehandler. Applications use of buffercontrol bytes is described in Section2, BuffeB}r Use. The remainder of thebuffer area is reserved for thebuffers. The use of the buffer areais decided upon by the handC}ler. Theapplication program has no definedway of directly accessing data inthis area.Man/Machine InterfaceIt is theD} responsibility of the massstorage media device to contain andload the XM301 handler along with therequired applications.E}The Six Standard Input/Output CommandInterfacesThe applications program accesses themodem handler by calling on CIO,F}which in turn, calls the handler.There are six I/O calls.(1) OPENAn OPEN command must be performedbefore any other mG}odem operations areallowed. Any of the IOCBs may beused. Aux1 specifies the I/Odirection: bit 2 for input; bit 3for ouH}tput; both for bidirectional.The directionality applies only tocommunications data; initializationparameters are passed inI} eitherdirection after any OPEN command.Aux2 is ignored by the handler.The device name is "T". The rest ofthe filenameJ} is ignored.The command flag (CMCMD) is set tozero by the handler during OPEN.(2) CLOSEThe CLOSE command terminateK}s the I/Oprocedure and releases the IOCB. Anydata waiting in the output buffer issent first. The buffer area is thenrelL}inquished and any input dataremaining in the buffer is lost.When the buffer area is empty, thephone is placed on hook.[M}System.Reset] produces similarresults to the CLOSE command exceptthat the output buffer is not sent.Refer to Section 2, HaN}ndler/OperatingSystem Interface, for details.The modem operation may be suspendedwithout closing the IOCB, allowingthe O}serial bus to continuecommunicating with other devices.This operation is described under theappropriate commands in SectioP}n 2,Parameters Passed As Data Strings.(3) INPUTAny INPUT or GET operation throughCIO will result in the modem handleQ}rbeing asked to provide data for theuser.If no data is available, the handlerwaits for a character. There is notime-oR}ut when waiting for receiveddata. This waiting is terminatedwhen either the [Break] or[System.Reset] key is pressed. TheS}waiting is also terminated if thecarrier is lost. Error 136 isreturned when the carrier is lost.If data has been receivT}ed, theHandler stores the characters in theinput buffer as the data is received(up to the buffer's capacity). TheCIO reqU}uest for data is thensatisfied from this FIFO buffer.(See Section 2, Buffer Use.)The modem is double-buffered, so thehaV}ndler has one character time toinput each character received.Communications data is processed forparity and for translatW}ion from ASCIIto ATASCII. These operations aredescribed under the appropriatecommands in Section 2, ParametersPassed As X}Data Strings.(4) OUTPUTAny PRINT or PUT operation to CIOwill result in one or more bytes forthe handler to hand to tY}he modem.This data is interpreted either asset-up commands and parameters, or ascommunications data, as controlled bytheZ} command flag byte CMCMD. (SeeSection 2, Parameters Passed As DataStrings.)Communications data is processed fortransla[}tion from ATASCII to ASCII,and then from parity. Theseoperations are described under theappropriate commands in Section 2\},Parameters Passed As Data Strings.Output bytes are received by thehandler and placed into the outputbuffer as fast as ]}the bytes come fromCIO. If the FIFO buffer fills, thehandler loops other character fromCIO until space becomes available ^}inthe buffer. There is no time-outwhen the handler is waiting forbuffer space. The looping is brokenwhen either the [Br_}eak] or[System.Reset] key is pressed. Aloss of carrier also breaks the loop,and returns Error 136. Any time the buffe`}r contains data,the modem continues to send until thebuffer is emptied.(5) STATUS (Combines with PEEK)The STATUS coma}mand causes the handlerto place four bytes of statusinformation in the Operating Systemstatus area DVSTAT through DVSTAT+3b}(02EA - 02ED). These four bytescontain error and status informationfrom both the modem and from thehandler. The applicac}tion program canthen PEEK at these four bytes.The four bytes contain the followingbit-encoded data:DVSTAT+0: Communid}cations Error FlagsThe internal flags corresponding tothe status bits in this byte arereset upon STATUS request.Bit 7e}: Framing error encountered onreceived data.Bit 6: Byte-level overrunencountered. The modem lost one ormore characterf}s due to slow interrupthandling. This is caused either byslow reading of data by theapplication, or by an incorrectlyprog}grammed main CPU.Bit 5: Parity error encountered onreceived data.Bit 4: Received data bufferoverflow. The received q}B%DOS SYSB*)DUP SYSB SRAMDISK COMB\AUTORUN SYSBHANDLER OBJB&HANDLER DOCdata bufferoverflowed because the applicationsprogram did not input data from thebuffer in time. If the receivedbuffer hr}as not been supplied, onlyerror bit 6 is set.Bit 3: Zero (Reserved forexpansion).Bit 2: Zero (Reserved forexpanss}ion).Bit 1: Zero (Reserved forexpansion).Bit 0: Illegal command (recognizedby handler). This error applies onlytt}o the most recent command. Thiserror is cleared upon acceptance of alegal command.DVSTAT+1: Modem Status FlagsBit 7u}: Carrier detect. 1 when thecarrier is present.Bit 6: Zero (Reserved forexpansion).Bit 5: Loop Test enabled. 1 v}whenAnalog Loopback Test is active.Bit 4: Originate/Answer. Zero =originate, 1 = answer.Bit 3: Auto-Answer. 1 = ew}nabled, 0= disabled.Bit 2: DTMF dialing. 1 for DTMFdialing. 0 for pulsedialing.Bit 1: Zero x} (Reserved forexpansion)Bit 0: Off hook. 1 when the phoneis off-hook. 0 when the phoneis on-hook.y}DVSTAT+2: All bits set to zero.(Reserved for expansion).DVSTAT+3: All bits set to zero.(Reserved for expansion).(6) z} SPECIAL (XIO)This call is not supported by thehandler. The handler returns Error92 (hex), 146 (decimal), Function Not{}Supported.Parameters Passed As Data StringsControl functions (i.e., settingtranslation and parity handling,sending a |}break signal, and dialingthe telephone) are handled by passingthe commands and parameters to thehandler as the output and }}input data.There are two types of commands:Those with parameters and thosewithout. Commands start with atwo-byte escap~}e saequence output tothe modem handler. This escapesequence identifies the start of thecommand and specifies the command.}If the command containsparameterbytes, they are sent immediatelyfollowing the escape sequence.In normal operation, the }CIO outputdeals only with communications data.The handler checks the OperatingSystem RAM area command flag byteCMCMD as i}t receives each output fromCIO. (CMCMD is fixed in theOperating System database at location0007.) If the flag is zero, t}hehandler treats the byte ascommunications data. If the flag isnonzero, the handler treats the byteas a command.When }the handler is not processing acommand, output bytes sent with CMCMDnonzero are checked for a command andare not transmitt}ed. The handlerstarts processing a command when: Itis not processing a previous command;CMCMD is nonzero; or the output }databyte received is ESC (1B hex, 27decimal). Once a command sequencestarts, the handler finishes thesequence regardless} of the state ofCMCMD. The number of output andinput bytes is constant for any givencommand (except the DIAL command).Wh}en the command bytes have beenpassed, the handler again checksCMCMD with each output byte.Commands start with two output} bytes:[Esc] followed by the command letter;and the commands with outputparameters containing those two bytesfollowed by }the parameter.The handler ensures proper sequencingof commands with output data byemptying the output buffer prior topr}ocessing the command. Thisoperation occurs when the command isaccepted (i.e., the command letter isaccepted). During thi}s output bufferdrain, communications inputcharacters are saved in the inputbuffer.With both the handler and modem,comm}unications being received areplaced in the input buffer even whencommands are being processed.Except with the BREAK comm}and, eachcommand below is completed when thehandler returns from accepting thefinal byte. Execution of a commandmay resu}lt in an error which isreturned by the handler to theapplication when the commandcompletes execution. (See Section 2,Erro}r Handling.)Illegal commands (command letter notvalid) produce Error 84 (hex) 132(decimal), an invalid command, andare }not processed.The commands are defined as follows:SET TRANSLATION: (A ASCII, 41 hex,65 decimal)Two bytes of parame}ter follow thiscommand. The first specifies thetranslation options. The second isthe will-not-translate substitutioncha}racter. Translation alwaysfollows parity checking on input, andalways precedes parity setting onoutput. The translation }options areinterpreted as follows:Bit 7: Ignored by the modem.Bit 6: When 1, specifies appendinglinefeed (0A hex, 1}0 decimal)whenever a Carriage Return (OD hex,13 decimal) is transmitted. This bitis ignored if bits 5-4 of thisparameter} byte are 10 or 11. TheCarriage Return character may comeeither from the untranslated ATASCIIgraphics character with code} OD hex,or from the translation of ATASCIIEOL (9B hex, 155 decimal) to CR.This translation option has no effecton input d}ata. The initializationdefault for this bit is 1.Bits 5 & 4: When 10 or 11, specifiesno translation. This optionsupp}resses bit 6.When 00, specifies minimal ("light")translation. On input, CarriageReturn (0D hex, 13 decimal) isconverte}d to EOL (9B, 155). Onoutput, EOL is converted to CR. Bit7 of code is cleared in both caseswith the exception of EOL (9B}, 155).When 01, specifies major ("heavy")translation. Codes whoseinterpretations in ATASCII do notcorrespond to the AS}CIIinterpretation are untranslatable.Codes below Blank (20 hex, 32decimal) and codes above Vertical Bar(7C hex, 124 decim}al) areuntranslatable, with the exception ofCarriage Return and EOL. CR and EOLare translated just as in mode 00.On outp}ut, untranslatable codes aresuppressed and not transmitted. Oninput, untranslatable codes areconverted to the will-not-tr}anslatesubstitution character supplied bythe user.Bits 3 - 0: Ignored by the modem.SET PARITY: (C ASCII, 43 hex, 67}decimal)One byte of parameter follows thiscommand. Bits 7 - 4: Ignored by the modem.Bits 3 & 2: Specify input pa}rityoperation. The input parityoperation precedes the translationoperation. 00 specifies no parityoperation. 01 specif}ies an oddparity check. 10 specifies evenparity checking. Should any paritycheck fail, the parity error statusbit is se}t. 11 specifies no paritychecking. In all but mode 00, theparity bit is cleared after thecheck. The parity bit is alway}s bit7 (high-order bit) of the 8-bit formof the character, regardless oftransmission byte size. The defaultfor these bit}s is 00.Bits 1 & 0: Specify output paritygeneration. The output parityoperation follows the translation.If LF is appe}nded to CR, each istreated separately for parity. 00specifies even parity. 11 specifiesforcing the parity bit to 1. The}parity bit is always bit 7(high-order bit) of the 8-bit form ofthe character, regardless oftransmission byte size. The d}efaultfor these bits is 00.END OF COMMANDS: (E ASCII, 45 hex,69 decimal)The handler sets the command flagCMCMD to z}ero when it receives thiscommand. The user has the option ofending command mode either by pokingCMCMD to zero or by inclu}ding thiscommand in the output.STATUS: (F ASCII, 46 hex, 70decimal)Performs the same function as the C10STATUS call} (DVSTAT through DVSTAT+3shall be filled in the OperatingSystem RAM area). This alternatestatus call is supplied forhigh}-level languages lacking the C10STATUS call. No data is returned inthe input stream.SET AUTO-ANSWER: (G ASCII, 47 hex,}71 decimal)The modem is set in the AUTO-ANSWERMode. (The default AUTO-ANSWER isdisabled.) Once Auto-Answer isenable}d, all subsequent incomingphone calls will be considered ascomputer connections. To disable theAuto-Answer use the [Esc][}T] command.BREAK: (H ASCII, 48 hex, 72 decimal)A BREAK signal is transmitted. Theexecution of this command is deferr}ed(control returns immediately and theBREAK is sent for the following500ms). Output data is buffereduntil the BREAK fini}shes.Since the BREAK transmission proceedsconcurrently as control is returnedto the caller, another command may begiven} to the modem handler before theBREAK is completed. Should thishappen, the handler finishes thebreak and transmits any ch}aractersbeing held in the output bufferbefore executing the new command.SET ORIGINATE: (I ASCII, 49 hex, 73decimal)}The modem is set in Originate Mode(the default).SET ANSWER: (J ASCII, 4A hex, 74decimal)The modem is set in Answer M}ode.DIAL DIGITS: (K ASCII, 4B hex, 75decimal) Used for pulse dialing.A string of digits to dial followsthis command}. Each digit is held inone byte. The handler ignores themost significant four bits of eachdigit byte, and interprets the}low-order bits as follows:0 - 9 Digit to dial, 0 through 9B End-of digitsC 3-second delayA,D},E,F, Ignored (reserved forfuture expansion)(Note: Digits may be representedin either ATASCII or BCD.)For pulse d}ialing, the controller isresponsible for inter-digit timing.After dialing each digit, the modemwaits the appropriate inter}-digittime before accepting the next digit.The controller dials each new digitas instructed to do so.For DTMF dialing, }the handler isresponsible for timing andtransmission of the DTMF tones bygenerating them from POKEY andtransmitting them }into the telephoneline.The end-of-digits characters arerequired to terminate each DIALDIGITS command. The handlerinte}rprets each character received asa digit for dialing until an XB (hex)character is received. (Note:ATASCII EOL, 9B hex, m}ay be theterminating character.)It is not required that the user diala complete telephone number with oneuse of the DIA}L DIGITS command. Theuser may use more than one DIALDIGITS command to dial a phonenumber. There will be no signal tothe} modem of the last digit of thecomplete phone number. The modemassumes each DIAL DIGITS command maybe the last, and monit}ors for thecarrier following each command. Themodem starts a thirty-second time-outfollowing each end-of-digits command.}If neither another DIAL DIGITScommand nor carrier is detected inthe period, the modem will place thephone on-hook.In DT}MF dialing mode, the computerresident handler passes dial tonesdirectly through the modem, andterminates the dialing seque}nce withthe thirty-second timeout "P"command, causing the wait for carrierdetect and subsequent actions(establishing line} connect ortime-out and going on-hook).GO OFF-HOOK: (L ASCII, 4C hex, 76decimal)The modem takes the phone off-hook.T}he modem then monitors for thecarrier (with thirty-secondtime-outs.GO ON-HOOK: (M ASCII, 4D hex, 77decimal)The mode}m places the phone on-hook(the default). This command is usedto terminate dialing, or to terminatewaiting for the carrier} followingdialing.SET PULSE DIALING: (N ASCII, 4E hex,78 decimal)The handler communicates dial digitscommands to th}e modem for pulsedialing (the default).SET TONE DIALING: (O ASCII, 4F hex,79 decimal)The handler performs dial digit}soperations itself by suspendingoperation of the modem on the SIOinterface, generating the tones usingPOKEY, resuming ope}ration of themodem, and invoking a thirty-secondtime-out using the "P" command.START THIRTY SECOND TIME-OUT: (PASCII, 5}0 hex, 80 decimal)The modem begins a thirty-secondtime-out for detecting a carrier.This command is used after generating}a tone-dialing sequence from thecomputer. If no carrier is detectedwithin thirty seconds, the modemplace the telephone o}n-hook.RESET MODEM: (Q ASCII, 51 hex, 81decimal)Reinitializes the modem controllercode.ENABLE SOUND: (Ru ASCII,} 52 hex, 82decimal)Turns sound to T.V. onDISABLE SOUND: (S ASCII, 53 hex, 83decimal)Turns sound to T.V. off. (Th}edefault)DISABLE AUTO-ANSWER: (T ASCII, 54hex, 84 decimal)Turns Auto-Answer mode off. (Thedefault)SET ANALOG LOO}P: (W ASCII, 57 hex,87 decimal)The Analog Loopback Test is turnedon.This command is used by anapplication with an a}ppropriateindication to the user as to whetherthe test has passed or failed.CLEAR ANALOG LOOP: (X ASCII, 58 hex,88 dec}imal)The Analog Loopback Test is turnedoff. This is the default state.RESUME MODEM OPERATION: (Y ASCII, 59hex, 89 d}ecimal)Communication with the modem isre-enabled. This command is used inconjunction with the SUSPEND command(see desc}ription below) to reallocatethe serial bus for communication withthe modem. Execution of this commandcauses CMCMD to set }to zero and fillsDVSTAT through DVSTAT+3 with currentstatus information.SUSPEND MODEM OPERATION: (Z ASCII,5A hex, 90 d}ecimal)Communication with the modem isdisabled. The nature of the serialbus protocol requires that no otherdevice may }use the serial bus whilethe modem is in an active (receiving)state. The SUSPEND command, unlikethe CLOSE command, maintai}ns all ofthe current modem settings (phonestays off-hook) including data whichmay remain in the user-supplied I/Obuffer. } Upon execution of thiscommand, the serial bus isrelinquished and the application cancommunicate with other peripherals.}While the modem is in the "suspended"state, only the RESUME MODEM and CIOCLOSE commands are considered validand processed} normally by thehandler. All other operationsrequested of the handler return theCIO error code for invalid command(84hex}, 132 decimal).Any information received by the modemover the telephone line while themodem is "suspended" will be lost.}It is the responsibility of theapplications software to guardagainst this possibility (i.e., byimplementing a flow-control}protocol).Error HandlingThree exceptional conditions mayoccur: Errors in calling on andcontrolling the modem;Commun}ications errors; andAsynchronous interruption ([Break]key and[System.Reset]). Errors ofthe first type always occur as a}result of an I/O call to the modemhandler through CIO. The errorcondition is signaled to theapplication via a CIO error re}turn.The second error type includes bufferoverrun, framing errors, parityerrors, and loss of carrier. Theseerrors occur }during the applicationwith a CIO error. Instead, theseerrors set internal error flags whichthe application may check with} theSTATUS command. (See Section 2, TheSix Standard Input/Output CommandInterfaces.) The third type of error,[System Re}set], results in an openIOCB to the modem. (See Section 2,Handler/Operating System Interface.)Certain errors may occur o}n any I/Ocall to the handler: ERRORFROM 80 hex (128 dec) [BREAK] key I/Oabort handler 85 h}ex (133 dec) IOCB not openCIO 86 hex (134 dec) bad IOCBspecified CIO 8A hex (138 dec) timeout (no mo}demresponse) handlerError 85 does not occur on OPEN orSTATUS since CIO performs an implicittemporary OPEN for the}se operations.Other errors are specific to certainI/O calls: CALL ERRORFROM OPEN 81 (129) IOCB already openCIO }84 (132) Invalid command (no I/Odirection) handler 96 (159) Port (modem) already openhandlerINPUT 83 (131)} Write onlyhandler 88 (136) EOF (means carrier loss)handlerOUTPUT 87 (135) Read onlyhandler 88 (136) EOF (means} carrier loss)handlerXIO 92 (146) Function not supportedhandlerOUTPUT 84 (132) Invalid command (notrecognized) } handlerestablish 98 (152) Illegaluser-supplied buffer handler[System.Reset] results in the closingof the mode}m IOCB. When the modemIOCB is closed, any data not yet sentfrom the output buffer will not besent. [System.Reset] affect}s thefile closing by "mashing" the systemto its reset state. This operationis described in Section 2,Handler/Operating S}ystem Interface.Buffer UseThe 256 byte input and 64 byte outputbuffer areas allow effectiveconcurrent operation betwe}en themodem performing full duplexcommunications and the 6502 CPUrunning an application. Theapplication may not, however}, use theserial I/O channel while the modem isactive. As the modem receives acommunications byte, it interruptsthe 6502.} The modem handler fieldsthe interrupt and saves the incomingcharacter in the input buffer. Dataheld in the buffer is su}bsequentlyread by the application via an inputcall through CIO to the modemhandler. Similarly, output datafirst goes int}o the output buffer.As the modem completes sending eachoutput byte, it interrupts the 6502for more data. The handler take}s theinterrupt and gives the next bufferedbyte to the modem for transmission.The modem handler is responsible forkeepin}g track of the data in thebuffers as the data arrives and issent. Status is maintained by thehandler, keeping track of ho}w muchdata each buffer holds at any time.The application program has access tothis information by PEEKing at it.Each buff}er is circular (a ring),holding up to one fewer bytes thanthe buffer's size. Each buffer isaccounted for by internal,use}r-transparent pointers. There aretwo byte-count bytes which may bePEEKed at by the application if itneeds to know the qua}ntity of databacklog. These counters are locatedas follows: Location $400 INCNT Number ofbytes currently in inp}ut buffer. Location $401 OUTCNT Count ofbytes currently in output buffer. The buffer area is alwaysformatted }the same, even if the modemis being used for INPUT only orOUTPUT only.The applications program may PEEK atINCNT and OUT}CNT to determine thenumber of bytes currently in theinput or output buffers. All otherparts of the buffer area are forha}ndler use only. There is nodefined way for the application touse any of this data.The output buffer is always 64 bytes}in length. As soon as data is putinto the output buffer, it is drainedby the handler at the maximum rate ofthe modem unti}l the buffer isemptied. Should the buffer fill, thehandler loops for space, waiting forthe modem, and returns to theappl}ication through CIO only when thebyte is placed in the buffer. If theapplication does not wish to be held,it will have to} check the buffer usebefore making the output request.The input buffer is 256 bytes inlength. It is drained by theappli}cation as fast as theapplication can handle the data,until the buffer empties. When thehandler is drained, it loops andw}aits for data from the modem. Ifthe application does not wish to beheld, it will check the buffer usebefore making the i}nput request.Should the buffer overflow, an errorflag will be set which may beinterrogated by the STATUS command.(See Sec}tion 2, The Six StandardInput/Output Command Interfaces.)Input buffer overflow indicates thatdata is lost. The handler re}tainsthe data in the buffer and discardsthe new data from the modem.Handler/Operating System InterfaceThe handler int}erfaces to theOperating System in the followingways: Initialization (cold start);System reset (warm start); Break keyfla }g; Interrupt handling (IRQ);System vertical blank timer, and CIO(including the "put byte" call bywhich the application byp }asses CIO).There are also a number of fixedbytes/words in the Operating SystemRAM area reserved for use by themodem modul }e handler.Calling interfaces between theapplication and the CIO, and betweenthe CIO and any handler, is describedin the } ATARI Home Computer SystemTechnical Reference Notes. Inaddition to operating under CIOaccess, the handler supports the PU }TBYTE entry made by 8K BASIC directly(bypassing CI). BASIC enters PUTBYTE with the A, X, and Y registersas set by CIO. H}owever, the zero pageIOCB is not established (exceptICAX1Z and ICAX2Z), and any checkingnormally done by CIO is bypassed a}ndperformed by the handler.The handler monitors the System Break key flag (BRKKEY) wheneverexecuting any loop which eit}hercontinues indefinately(as whenwaiting for the modem where there isa possibility the modem may notrespond), or whenever} the loop mayexceed one second. If the [Break]key is detected, the handler returnsto the caller with Error 80(hex).(See }Section 2, Error Handling.)The handler/modem interface isdesigned so that pressing the [Break]key does not produce any u}ndesirableside effects. (Preferably, the modemshould abort an operation when the[Break] key is pressed at the sametime as} the handler aborts.)The handler includes code forfielding the IRQs which are generatedby the modem. The handler'sinte}rrupt code address is installedin the Operating System RAM vectors(Serial Input Ready, Serial OutputRead, Serial Output Co}mplete) whenthe modem is OPENed or, subsequent toOPEN, when the modem operation isRESUMEd. The handler contains aspecial} serial bus driver for themodem. When the modem is CLOSEd orSUSPENDed the handler reinstalls theOperating System RAM inte}rrupt vectorfor Serial Input Ready.The power-on default conditions areas follows: All errors are cleared;translation a}nd parity controls areset to zero; and the Analog LoopbackTest is off.The effect of a warm-start([System.Reset]) is to }close any fileopen to the modem and to reinitializethe handler and modem to thepower-on.arm-start([System.Reset]) is to \