NCR 7454 - Diagnostics

6-2 Chapter 6: NCR 7454 4x20 Customer Display
Diagnostics
Power‐UpDiagnosticsoccursoonafterthehardwareresetcircuitryis
released,orwhenaResetDisplaycommandisreceivedfromthehost
software.Whenthehardwareispowereddown,allregistersand
memoryarelost.Thedisplayisnotcapableofanykindofpower
recoverybacktoaprevious
state.AsapartofthePower‐Up
Diagnostics,theworkingregistersandvariablesareinitialized(setto
zero).
Theself‐diagnosticsinclude:
1. Micro‐controllerTest
TheBusylineissetactiveatthebeginningofthetest.Thefirsttest
isExclusive‐ORingallin ternalprogram memorylocations
andthe
resultofthetestiszero.Anyunusedbytesinthesummedpageare
alwaysprogrammedwithnullvaluessothattheydonothavean
impactontheexecutionofthetest.AninternalRAMtestwritesa
varyingnumericalvaluetoeachRAMlocation.Thepatternmust

showthatallRAMlocationscanbeuniquelyaddressed.AllRAM
willbewritten.Afterthewritephaseiscomplete,areadphase
beginstoensurethewritesheld.Ifanerrorisdiscovered,testing
haltsandthefirmwarebeginsexecutingaforeverdonothingloop.
2. DisplayTest
The
displaywillrunanextratestthatturnsonallpixelsonthe
display(charactercells)forabouttwosecondsandthendisplays
thepartnumberandthefirmwareversion“008‐0221552,V1.00.01”
foranothertwoseconds.Thispermitsausertoexaminethedisplay
foranypixelfailure.Theunit
doesnothavethecapabilityto
determineiftheDisplayTestpassed.Oncediagnostictestingis
completed,thelinestateswillbereturnedtonormalandthe
firmwarebranchestoitsidleroutine.
Note: WhentheI/FreceivesaResetcommand,onlyStep1is
executed.TheDisplayTestisnot
executed.