NCR Decision Mate V - Use O F Ports; Pow Er-Up Check; The Status Byte

USE OF PORTS
The Mouse Interface uses the f i r s t two addresses of the
eight available under an IFSEL number. I f the IFSEL number
is 2A (the default s ettin g), then these two ports are 30H
(Port 1) and 31H (Port 2). The significance of these ports
is as follows:
IN Port 1
OUT Port 1
IN Port 2
OUT Port 2
Read data from Mouse Interface.
Write data to Mouse Interface.
Read the Mouse Interface status byte.
Write commands to the Mouse Interface.
POWER-UP CHECK
When you switch on the computer with the Mouse Interface
inserted, the signal which resets the whole system also
in itia te s the loca l processor in the Mouse Interface to
execute instructions read from its own read-only memory
(ROM). These instructions include an integrity check of both
the ROM it s e lf and the read/write memory (RAM) on the Mouse
In t e r fa c e component board. The I/O ports are then
in itialized.
Should the Mouse Interface register a fault in ROM or RAM,
the appropriate b it o f the status byte is set. Otherwise
these two bits are set to zero. The follow in g section
includes information about how to read and evaluate the
status byte.
THE STATUS BYTE
Your program can read the status byte by means of an IN
instruction to Port 2 of the two ports used by the Mouse
In t e r fa c e . Figure 2.1 shows the s ig n ific a n c e o f the
individual bits within this byte.
MOUSE-6