Specifications

ADDITIONAL LOCAL IO FUNCTIONS
9-14 PP 41x/03x
9.12 PORT 80
A header (S1 – see Figure A-1) has been provided for monitoring data written to I/O Port 80 and
I/O Port 81. The PC BIOS writes status bytes to Port 80 that indicate a boot progress status and/or
highlight any faults found. Data written to this port can be monitored using a Logic State Analyzer
(LSA) or seven segment hexadecimal displays. See Section A.5.9 for details of the connector used
for this port.
The PC BIOS also writes status information to Port 81. Further details are beyond the scope of this
document.
After boot-up this port can be used to monitor other status bytes written to Port 80 and Port 81,
which can be useful for debug purposes.