How your Iaserprinter communicates
YourcomputercommunicateswiththeStar LaserPrinter8througheithera
parallelcableor one of twokinds of serialcable.The printer’sinterj2ace,
the link or boundaryit shares with your computer,defineswhether the
printerwillacceptcharactersandcommandsfromyourcomputerone byte
orone bit at atime.
Abitis thesmallestunitof computerorprintermemory.Ithas eitheralow
orhighelectriccharge,whichwe representwiththedigitsOand 1.Usually
eight adjacentbits are grouped to form abyte. Sinceabyte normally
representsonecharacter,thisstringofbits- O1OOOOO—mightrepresent
theletterA.
Theserial interfaceacceptsjust one bit at atime fromyour computer.A
parallelinterfacecanhandleawholebyteatonce,bymovingdatabitsside-
by-sidealongseparatewires.Youchoosewhichinterfacemethodyouwant
to use by selectingit on the operator panel,as explained in your Star
LaserPrinter8OperationsManual.
The Star LaserPrinter 8is acomputer
TheStar LaserPrinter8firstmapsthecharactersto be printedintoits own
randomaccessmemory(RAM).Thatis,theprinterbuildsa“picture”in its
memorycorrespondingto thepageyou wanttoprint.Whenthat’s donethe
pnntercanreproducethepageontopaperon itsown,lettingyourcomputer
geton’withother work.
YourStarLaserPrinter8comeswithone megabyteofRAM—theequiva-
lentof aboutone millioncharacters.AStarLaserPrinter8optionletsyou
addasecondmegabyteofRAMif,say, youneedto mapfull-pagegraphics
orstoremore fonts. AccompanyingallthatRAMisanother512 kilobytes
ofread onlymemory(ROM),containingalibraryofinternalfonts andthe
programsthatlet theStar LaserPrinter8emulateotherprinters.
AMotorola68000computerchipcontrolsboththememoryandtheprinting
mechanismintheprinter,calledtheprintengine.Theprintcrstoresawhole
pagein RAM before printingit. (If apage is so densethat it overflows
memory-a mostunlikelyevent—theStarLaserPrinter8printsthepageon
twosheets.)
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