Parallel Port Error Codes; Level O Loop Tests On Generic Processor Board - NCR PC4i Service Manual

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LEVEL O DIAGNOSTICS
"Check Keyboard" section of chapter 2 "Basic
Troubleshooting".
PARALLEL POBT ERROR CODES
The power-on diagnostics/initialization routines also
issue a set of two character hexadecimal codes to the
MPB parallel port. These enable a technician to
attach the Parallel/Serial Test Adapter (see "Tools",
Chapter 1) and/or an oscilloscope to the parallel
port and display these codes to obtain an indication
of hardware problems and status. This technique is
quite valuable when, for any reason, the programs are
unable to display messages on the screen.
LEVEL O LOOP TESTS ON GEBERIC PROCESSOR BOARD
After turning on the computer its hardware is tested
in a sequence of test routines before booting the
operative system. There exist two groups of tests,
the first group is always run, whereas the second
group is only executed when Level O Loop has been
selected. After completion the test sequence is
concluded by the booting procedure, if no Level O
Loop mode has been chosen.
With the Keyboard Adapter (See "Tools", Chapter 1)
plugged or the disk drives disconnected from the MPB
the Level O Loop Diagnostics are selected. The
Parallel/Serial Test Adapter (see "Tools", Chapter 1)
is provided with 8 LEDs on which error messages are
issued as error codes (see
Fig.
1-3 "Table of Error
Messages" Before selecting the Level O Loop Mode the
jumpers 3 and 4 of the SWA switch block on the
"Alternate" MPB have to be in ON position and the
Parallel/Serial has to be plugged into the respective
receptacle.
As soon as the Level O Loop Diagnostics encounters an
error while running the test, the test procedure is
repeated and the respective error message is issued
on the LEDs or displayed and/or on screen.
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