Troubleshooting and Repair 6-9
Beep
Code
Diagnostic
Code
Description
Test Performed
4-2-2
35h
Shutdown test in progress or
failure.
A return address is stored in 40:67h and the
processor is reset via the keyboard controller. If
a timer tick occurs during this time period, an
error message is displayed on the screen.
Other failures are hard to detect. If possible, the
BIOS will continue with POST, skipping the
memory tests.
4-2-3
36h
Gate A20 failure.
To test extended memory, the processor must
be placed in protected mode and the A20 line
must be enabled. For the memory tests, the
BIOS generally uses the keyboard controller to
enable A20. If the A20 line is not properly set
during the memory test, an error message is
displayed on the screen and the memory test
are suspended. The system does not halt.
4-2-4
37h
Unexpected interrupt in
protected mode.
During the memory tests, the processor is
placed in protected mode. All interrupts in the
interrupt descriptor table are initialized to point
to special handler that displays a message on
the screen. All hardware interrupt are disabled.
The system does not halt when an unexpected
interrupt occurs.
4-3-1
38h
RAM test of memory above
64K in progress or failure.
The memory above the first 64K is tested with a
rolling ones test and a pattern test. All success
and failure messages are displayed on the
screen and POST will continue.
4-3-2
3Ah
Programmable interval timer
channel 2 test in progress or
failure.
Over a period of time, the current count values
in timer 2 are read and accumulated by ORing
them into the values read so far. It is expected
that during the time period, all bits will be set. If
an error is detected, an error message will be
displayed on the screen and POST will
continue.
4-3-4
3Bh
Real-time clock test in
progress or failure.
Over a period of time, the Update-In-Progress
bit of Status Register A of the real-time clock is
read and tested. The bit should toggle from 0 to
1 within the time period.
4-4-1
3Ch
Serial port test in progress or
failure.
Pattern test of one or more of the installed
serial ports. If a failure is detected, an error
message will be displayed and POST will
continue.
4-4-2
3Dh
Parallel port test in progress
or failure.
Rolling ones test is done to one or more of the
installed parallel ports. If a failure is detected,
an error message will be displayed and POST
will continue.
4-4-3
3Eh
Math coprocessor test in
progress or failure.
An integer load and store is performed with the
math coprocessor. If the values do not match,
an error message will be displayed and POST
will continue.
