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 internal 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.
