3-8 Troubleshooting and Repair
Table 3-3 BIOS Beep Codes
Beep
Code
Diagnostic
Code
Description
Test Performed
3-1-2
21h
Master DMA register test
in progress or failure.
Pattern test of channels 1 through 3 of
the master DMA controller (starting port
address = C4h). Failure results in a
system halt.
3-1-3
22h
Master interrupt mask
register test in progress or
failure.
Rolling ones and zeros tests of the
mask register of the master
programmable interrupt controller (port
21h). Failure results in a system halt.
3-1-4
23h
Slave interrupt mask
register test in progress or
failure.
Rolling ones and zeros tests of the
mask register of the master
programmable interrupt controller (port
A1h). Failure results in a system halt.
none
25h
Interrupt vector loading in
progress.
No specific test is performed - just
indicates that the Interrupt Vector table
is being initialized.
3-2-4
27h
Keyboard controller test in
progress or failure.
The self-test command (AAh) is issued
to the 8042 (keyboard controller) and
the results are monitored. Failure
results in a system halt.
None
28h
CMOS RAM power failure
and checksum calculation
test in progress.
The power-fail bit in CMOS RAM is
tested and the lower CMOS RAM area
is being checksummed. A failure does
not result in system halt.
None
29h
CMOS RAM configuration
validation for video in
progress.
No specific test is performed - just
indicates that the configuration
specified in CMOS for video is being
matched against the actual installation.
A failure does not result in a system
halt.
3-3-4
2Bh
Screen memory test in
progress or failure.
The video buffers (B0000h and
B8000h) are tested with a pattern test
and a rolling ones test. Failure will
result in a beep code but not a system
halt.
3-4-1
2Ch
Screen initialization in
progress.
Until the video installation is confirmed,
any calls to INT 10h Function 0 (set
mode) will be prefaced with the
diagnostic code. There is no expected
failure from this.
