HP Vectra Technical Reference Manual page 202

To verify that the command has been read, the software can read the ISF bit in the status
register of the controller.
The 8041 transfers data and commands to the logical keyboard driver through the SVC (Service)
port (I/O address 69H). When data is present on this port, the 8041 issues an interrupt alerting
the 8041 interface driver of the data. The 8041 interface driver reads the data from the SVC
port, then writes any value to the Acknowledge port (I/O address 6AH) which sends an
acknowledge signal to the 8041 and clears the interrupt. Table 5.24 defines the SVC Register
request functions.
Keyboard 193