1.2.3Howyour Iaserprinter communicates
YourcomputercommunicateswiththeStar LaserPrinter4througheither
apardef cableorone oftwokindsof serialcable.Theprinter’sinterjzce,
the link or boundaryit shares withyour computer, defineswhetherthe
printerwillacceptcharactersandcommandsfromyourcomputeronebyte
orone bit at atime.
Abitis thesmallestunitofcomputerorprintermemory.It haseitheralow
orhighelectriccharge,whichwe representwiththedigitsOand 1.Usually
eight adjacentbits are grouped to formabyte. Since abyte normally
representsonecharacter,thisstringofbits- O1OOOOO1—mightrepresent
theletterA.
Theserial interfaceacceptsjust onebit at atime fromyour computer.A
parallelinterfacecanhandleawholebyteatonce,bymovingdatabitsside-
by-sidealongseparatewires.Youchoosewhichinterfacemethodyouwant
touse byselectingit onthecontrolpanel,as explainedinyourStar Luser-
Printer4OperationsManual.
1.2.4The Star LaserPrinter4isacomputer
TheStar LaserPrinter4firstmapsthecharactemtobe printedintoits own
randomaccessmemory(RAM).Thatis,theprinterbuildsa“picture”inits
memorycorrespondingtothe pageyouwantto print.Whenthat’sdonethe
printercanreproducethepageontopaperonits own,lettingyourcomputer
geton with otherwork.
YourStarLaserPrinter4comeswithonemegabyteof RAM—theequiva-
lentof aboutone millioncharacters.AStarLaserPrinter4optionletsyou
addasecondmegabyteofRAMif,say, youneedtomap full-pagegraphics
orstem morefonts. AccompanyingallthatRAMisanother512 kilobytes
ofread onlymemory(ROM),containingalibraryofinternalfonts andthe
programsthatlet theStar LaserPrinter4emulateotherprinters.
An Intel 80960KAcomputer chip controlsboth the memory and the
printingmechanisminthepnnter,calledtheprintengine.Theprinterstores
awholepage in RAM before printingit. (If apage is so dense that it
overflowsmemory-a mostunlikelyevent—theStarLaserPrinter4prints
thepage ontwo sheets.)
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