3-10 Troubleshooting and Repair
Table 3-3 BIOS Beep Codes
Beep
Code
Diagnostic
Code
Description
Test Performed
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 of the
installed parallel ports. If a failure is
detected, an error message displays.
