I/O Ports - IBM AT 5170 Technical Reference

FO-FF
Pulse Output Port-Bits 0 through 3 of the controller's
output port may be pulsed low for approximately 6
microseconds. Bits 0 through 3 of this command indicate
which bits are to be pulsed. A 0 indicates that the bit
should be pulsed, and a 1 indicates the bit should not be
modified.
Note: Bit 0 of the controller's output port is
connected to System Reset. Pulsing this bit resets
the microprocessor.
I/O Ports
The keyboard controller has two I/O ports, one assigned for
input and the other for output. Two test inputs are used by the
controller to read the state of the keyboard's
I
clock
I
(TO) and
I
data
I
(Tl) lines.
The following figures show bit definitions for the input and output
ports, and the test-inputs.
1-54 System Board