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.
