AT&T PC 6300 - Page 219

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DIAGNOSTICS
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4. The Display Controller Board is programmed for
monochrome 80 by 25 text mode.
5. The parallel printer port and the display are used to report
the successful completion of each diagnostic test. The check
point bytes are not strobed to the parallel port, so that an
attached printer will not confuse the check point
information with actual printable data.
6. The parallel printer port and the display are sent
confirmation that the CPU test has been successful. If the
CPU test fails, an attempt is made to send a "CPU (i8086)
Fail" error message to the display, and the CPU is halted.
7. The ROM test is performed by calculating a checksum. The
checksum, defined to be a "byte addition of all the bytes in
the high and low ROM modules, is summed and compared to
zero.
8. The parallel printer port and the display are sent
confirmation that the ROM module test has passed. If the
ROM test fails, a "ROM Module Fail" error message is sent
to the display, indicating that the system diagnostic/boot
strap ROM is faulty and the CPU is halted.
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