T e c h n i c a l I n f o r m a t i o n
5-42 OWNER’S HANDBOOK
I/O Map
I/O Address
Port
0800h : write
Port 80 Diagnostic Port
0120h
2
: write
BIOS page register
0120h : read
Status register
0121h : write
DOS Flash page register
0122h : r/w
Control register
0123h 0127h
Reserved for expansion
0128h 012Fh
Diagnostic UART
03E8h 03EFh
COM3
02E8h 02EFh
COM4
= Unused portion of memory
Port 80 Monitor : 0080h : write
This 8-bit port captures all diagnostic codes written by the motherboard
BIOS. The port is readable by DiagP, which can then communicate the
codes to the SMC. If the port contents are lost due to overrun by the
motherboard, there is no problem; the aim is merely to keep track of the
last value in the event that the system hangs.
When the port is written, the DiagP must be informed through an
interrupt line (PORT80_IRQ).
When the DiagP reads the port, the interrupt line must be automatically
reset.
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