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Chapter 3: Programming Commands76

Preferred implementation

ForanewapplicationtheGS(1D)sequencesarerecommendedtoavoidpossiblemisinterpretationofaDLE(0x10)

sequenceasaclearprinter(0x100,ASCIIDLENUL)command.

AnapplicationusingtheseGS(1D)sequences,doesnotneedtodistinguishfortheprinterbetweenthenewrealtime

commandsandtheclearprintercommand.Thisimplementationisidealforanexistingapplicationthatalreadyusesthe

clear printer command or for a new application being developed.

Alternate implementation

ThealternateimplementationusestheDLE(0x10)sequencesasimplementedonotherprinters.Anapplicationusingthese

DLE(0x10)sequencesandtheoriginalclearprintercommand(0x10)mustdistinguishfortheprinterbetweenthenewreal

timecommandsandtheclearprintercommandbyaddingaNUL(0x00)totheclearprintercommand.

AnapplicationusingtheseDLE(0x10)sequencesmustalsosendthesecondbyteofthesequencewithin100milliseconds

oftherst,topreventtherstbytebeingmistakenforaclearprintercommand.

Rules for using real time commands

Three situations must be understood when using real time commands.

First,theprinterexecutestherealtimecommandwithinafewmsecofdetectingitintheinputbufferandwilltransmit

statusregardlessoftheconditionoftheDSRsignal.

Second,theprintertransmitsstatuswheneveritrecognizesarealtimestatustransmissioncommandsequence,evenifthat

sequencehappenstooccurnaturallywithinthedataofanothercommand,suchasgraphicsdata.

Inthiscasethesequencewillalsobehandledcorrectlyasthegraphicsdataitisintendedtobewhenthegraphics

commandisexecutedfromthebuffer.

Third,caremustbetakennottoinsertarealtimecommandintothedatasequenceofanothercommandthatconsistsof

twoormorebytes.

Inthiscasetheprinterwillusetherealtimecommandsequencebytesinsteadoftheothercommand’sparameterbytes

whennallyexecutingthatothercommandfromthebuffer;theothercommandwillNOTbeexecutedcorrectly.

ThesethreesituationsgenerallyprecludeuseofstandardDOSdriversfortheserialcommunicationportswhenusingreal

time commands.

Moving data through the buer

ApplicationsshouldnotletthebufferllupwithrealtimecommandswhentheprinterisbusyattheRS-232Cinterface.

AbusyconditionattheRS-232Cinterfacecanbedeterminedbybit3oftheresponseto1D05,or1D041,or10041.

Thereasonforaparticularbusyconditioncanbedeterminedbyotherresponsesto1D04nor1004n.

Althoughtheprinterrespondstorealtimecommandswhenitisbusy,itwillplacethemintothebufferbehindanyother

datathere,andushthemoutintheorderinwhichtheywerereceived.Whentheprinterisbusyduesimplytobufferfull

(thatis,itcan’tprintdataasfastasitcanreceiveit),thendatacontinuestobeprocessedoutofthebufferatapproximately

printspeedandtherealtimecommandswilleventuallygetushedout.

Whentheprinterisbusyduetoanerrorcondition,thendatastopsbeingprocessedtothebufferuntilthecondition

clearsonewayoranother.Ineithercase,butmorequicklyinthecaseofanerrorcondition,thebuffercanllwithreal

time commands.

WhentheDLE(0x10)sequencesarebeingused,thelastbytestoredwhenthebufferllsupcouldbetheDLE(0x10)

code,withnoroomforthesubsequentEOTorENQ.WhenthisloneDLE(0x10)byteisnallyprocessedoutofthebuffer

it will be interpreted as a clear printer command.

Similarly,whentheGS(1D)sequencesarebeingused,thelastbytestoredwhenthebufferllsupcouldbetheGS(1D)

code,withnoroomforthesubsequentEOTorETXorENQ.WhenthisloneGS(1D)byteisnallyprocessedoutofthe

bufferitwillusethenextbyte,whateveritis,asthesecondbyteinitsGS(1D)sequence.

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