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