Sharp MZ-80B Owner's Manual page 133

124
An interrupt control word is next sent to the port:
Do
0
0
Enable OR Active Mask
Interrupts Logic High Follows
Interrupt control
The mask word following the interrupt mode word is:
0
0 0
Selects AS , A3 and AO to be monitored
Now, if a sensor puts a high level on line A
5 ,
A
3
,
or A
0
,
an interrupt request will be generated . The mask word may
select any combination of inputs or outputs to cause an interrupt. For example, if the mask word above had been:
0 0 0
0
I
then an interrupt request would also occur if bit A
7
(Special Test) of the output register was set.
Assume that the following port assignments are to be used:
EOH = Port A Data
ElH =Port B Data
E2H = Port A Control
E3H =Port B Control
All port numbers are in hexadecimal notation. This particular assignment of port numbers is convenient since A
0
of the
address bus can be used as the Port B/A Select and A
1
of the address bus can be used as the Control/Data Select. The
Chip Enable would be the decode of CPU address bits A
7
thru A
2
(1110 00). Note that if only a few peripheral devices
are being used, a Chip Enable decode may not be required since a higher order address bit could be used directly .