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24
Checkpoint
Beep Code
Code
14h
16h
1-2-2-3
17h
18h
1Ah
Description
Verify that the 8742 keyboard controller is
responding. Send a self-test command to
the 8742 and wait for results. Also read the
switch inputs from the 8742 and write the
keyboard controller command byte.
Verify that the ROM BIOS checksums to
zero.
Initialize external cache before autosizing
memory.
Initialize all three of the 8254 timers. Set the
clock timer (0) to binary count, mode 3
(square wave mode), and read/write LSB
then MSB. Initialize the clock timer to zero.
Set the RAM refresh timer (1) to binary
count, mode 2 (Rate Generator), and read/
write LSB only. Set the counter to 12H to
generate the refresh at the proper rate. Set
sound timer (2) to binary count, mode 3,
and read/write LSB, then MSB.
Initialize DMA command register with these
settings:
1. Memory to memory disabled
2. Channel 0 hold address disabled
3. Controller enabled
4. Normal timing
5. Fixed priority
6. Late write selection
7. DREQ sense active
8. DACK sense active low
Initialize all 8 DMA channels with these
settings:
1. Single mode
2. Address increment
3. Auto initialization disabled (channel 4 -
Cascade)
4. Verify transfer
3 Getting Started
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