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Data Communication from Printer to Host
Nibble Mode
Inthis mode, data istransferred between theprinterandthe hostthrough theprocedure described below.
Thestepsbeginningfrom(1)areapplicablewhentheNegotiationphasehasswitchedtotheHostBusyDataAvailablephase.If
the Negotiation phase hasswitched to theHost BusyData Not Available phase, the procedurestartsat step (9).
(1)After the negotiationsfortheentryintoNibblemodearecompleted,thehostsetsHostBusy(nAutoFd)toLow toindicate
that itisready toreceive data from theprinter.(Event 7)
(2)Theprinterplacesthelow-orderfourbitsonthereversechanneldatalineandsetsPtrClk(nAck)toLow.(Events8and9)
(3) The host sets HostBusy (nAutoFd)toHightoindicate that it has latched data andreceivedthesignal inEvent 9. (Event
10)
(4) The printersets PtrClk (nAck) toHigh.Thiscompletes transfer ofthefirst nibble. (Event 11)
(5) Steps (1)to(3)are repeated totransferthe high-orderfourbits, before proceeding tosteps (6)andon.
(6)AfterthehosthassetHostBusy(nAutoFd)toHigh (Event10)and receiveddata,theprinter mustsetthe four status lines
as shownbelow.(Event 13)
•PtrBusy(Busy) :Returnedtothe status given in Forwardmode.
•nDataAvail (nFault) : Setto Lowifthere is data tobesent.
•AckDataReq(PError) :SettoLowifthere isdata tobe sent.
•Xflag (Select) : Setto thecurrent mode (i.e., setto Low).
(7) The printersets PtrClk (nAck) toHigh.(Event 11)
(8) After Event11, thehostchecks thesignals set by theprinterinEvent 13. With thischeckthe host determines:
1.Whetherthere ismore data tobe sent from theprintertothehost;
2.Andwhetherdata canbe transferred from the hosttothe printer.
(9) If there isno more data tobe sent from the printer after thetransferofone byte (two nibbles),the host chooses oneof
threestatusselections:
1.Performing Termination andreturning to theCompatibility mode.
2.Remaining inthe Host BusyData Not Available phase.
3.SettingHostBusy(nAutoFd) toLow (Event 7)andmoving totheReverse Idle phase.
(10) If there ismore data tobe received fromthe printer,thehost chooses oneofthree status selections:
1.SettingHostBusy(nAutoFd) toLow andindicatingthat thehostis ready toreceive.
2.Remaining inthe Host BusyData Available phase.
3.Performing Termination andreturning to theCompatibility mode.
(11) If thehost selected theHost BusyData Available phase andset HostBusy (nAutoFd)toLow,the printer repeats the
stepsfrom (2) onwards.
(12)IfthehostselectedtheReverseIdlephaseandnew data becomes availabletobe sentfrom theprinter, theprintersets
PtrClktoLowtorequestthe host for aninterrupt. (Event 18)
(13) The printersetsPtrClk backtoHigh.(Event 19)
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