IBM AT 5170 Technical Reference page 69

AC
Diagnostic Dump-Sends 16 bytes of the controller's
RAM, the current state of the input port, the current
state of the output port, and the controller's program
status word to the system. All items are sent in scan-code
format.
~
AD Disable Keyboard Feature-This command sets bit 4 of
the controller's command byte. This disables the
keyboard interface by driving the clock line low. Data
will not be sent or received.
AE
Enable Keyboard Interface-This command clears bit 4
of the command byte, which releases the keyboard
interface.
CO
Read Input Port-This commands the controller to read
its input port and place the data in its output buffer. This
command should be used only if the output buffer is
empty.
DO
Read Output Port-This command causes the controller
to read its output port and place the data in its output
~
buffer. This command should be issued only if the output
buffer is empty.
Dl Write Output Port-The next byte of data written to I/O
address hex 60 is placed in the controller's output port.
Note: Bit 0 of the controller's output port is
connected to System Reset. This bit should not be
written low as it will reset the microprocessor.
EO
Read Test Inputs-This command causes the controller
to read its TO and T1 inputs. This data is placed in the
output buffer. Data bit 0 represents TO, and data bit 1
represents Tl.
System Board 1-53