Data Communication and Host Modes
Rev 3.0B Feb.08 59
•TCPautoanswerisenabled(S1),aTCPconnectionrequest
isreceived,andthemodemisnotinadatasession.
•Dataisreceivedontheserialportand
·TheStartupModeDefault(MD)is4(autoTCP)
·TheremoteTCPdestination,asdefinedinS53,success‐
fullyrespondstotheTCPconnectionrequest.
ThevalueofS7(TCPConnectionTime‐out)specifiesthe
numberofsecondstowait,afterinitiatingaTCPconnection
attempt,forasuccessfulconnectiontobeestablished.Ifthe
connectionhasnotbeensuccessfullyestablishedbeforethe
time‐outoccurs,ERROR/BUSYisreturned.
TCPpacketassemblyisaffectedbythevaluesofS50(PAD
ForwardingTime‐out)andS51(PADForwardingCharacter).
Datareceivedintheserialbufferwillbetransmittedwhenthe
idleinter‐charactertime‐outspecifiedinS50(intenthsof
seconds)occursorwhenacharacterisreceivedthatmatches
S51(ifnon‐zero).
TheTCPsessionwillbeterminatedifnodataistransmittedor
receivedforthetimeintervalspecifiedinTCPTandTCPS.
TCPTisthenumberofminutes(TCPS=0)orseconds(TCPS=1)
usedforthisidletime‐out.
Caution: TCPT should never be 0 when using the TCP mode. A
broken TCP session can result in the modem being left with a TCP
half-open connection that can only be terminated with a reset.
TCP Auto Answer
TCPautoanswer(S0=1|2)alsoallowsaTCPconnection
requesttobe“answered”whenthemodemisidle,notina
datasession.TheTCPconnectionrequestʹsdestinationport
hastomatchthemodemʹsdeviceport.
Note: UDP auto answer may also be set simultaneously with TCP
auto answer. Then, when in the idle state, the modem will accept
either a TCP connection request or UDP incoming packet, and enter a
TCP or UDP session as appropriate.
Hybrid ModesHybridmodesaresupportedmainlyforlegacyimplementa‐
tions.Someprevioushybridmodes(MD=5,6)arenolonger
implementedasspecial,uniquemodes.NowthatUDPauto
answer(UDPHalf‐open,S82=2)canbeenabledinconjunction