Input Line; Hp-Hil Interface - HP Vectra Reference Manual

The second line, RC, resets the 80286 when pulsed low. It is used
to return the processor to the real-address mode from protected
mode or to reset the system in response to a Control-Alt-Del.
The A20_GATE either enables the 80286 address line A20 (when
high) or forces it to a logical 0 (when low). It is used to cause
80286 addresses above 1 Megabyte to wrap when operating in
the real-address mode. Also, the 8041 writes to port 69H.
Input Line
The keyboard controller has an input line (KBINH) which is used by
the optional keylock keyboard inhibit switch. This front-panel
switch allows keyboard operation to be inhibited by turning the
key to the lock position. When locked, the keyboard responses
will still be returned, but scan codes from the keyboard will not be
returned by the 8041 .
HP-HIL Interface
The keyboard (and other input devices) are connected to the HP
Vectra via a 4-pin HP-HIL interface connector. See table 4.1 for the
pin assignments. The Serial In and Serial Out signals are connected
to the HP-HIL controller (U777), which is an integrated circuit
developed by Hewlett-Packard to control the HP-HIL. The HP-HIL
controller converts parallel data from the 80286 into serial data
on the HP-HIL, and conversely, converts serial data from the input
devices into parallel data to be read by the 80286. Approximately
60 times per second, the HP-HIL controller polls the input devices
to read any input they may ready, and to send commands and
data to the devices. After receiving data from one or more input
devices, the HP-HIL controller interrupts the 80286 by asserting
"CERBINT", and then the 80286 reads the data from the HP-HIL
controller.
Keyboard Interface 57