Z80 Datasheet, PDF (222/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

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Control Interface
A typical control mode application is illustrated in Figure 16. In this
example, an industrial process is to be monitored. The occurrence of any
abnormal operating condition is to be reported to a Z80 CPU-based control
system. The process control and status word has the following format:
D7
Special
Test
D6
Turn On
Power
D5
D4
Power
Halt
Failure Alarm Processing
D3
Temp.
Alarm
D2
Turn On
Heaters
D1
Pressurize
System
D0
Pressure
Alarm
The PIO may be used as follows. First, Port A is set for Mode 3 operation
by writing the following control word to Port A.
D7 D6 D5 D4 D3 D2 D1 D0
1 1 X X 11 11
Whenever Mode 3 is selected, the next control word sent to the port must
be an I/O select word. In this example, port data lines A5, A3, and A0 are
selected as inputs, and the following control word is written:
D7 D6 D5 D4 D3 D2 D1 D0
0 01 0 1 0 0 1
Next, the appropriate interrupt vector must be loaded (refer to the Z80 CPU
User’s Manual for details):
D7 D6 D5 D4 D3 D2 D1 D0
V1 V6 V5 V4 V3 V2 V1 0
An interrupt control word is next sent to the port:
D7 D6
10
Enable OR
Interrupts Logic
D5 D4 D3 D2 D1 D0
1 1 01 11
Active Mask
High Follows
Interrupt Control
The mask word following the interrupt mode word is:
UM008101-0601
Parallel Input/Output