ZiLOG Z8 CPU, User Manual

Page: 105 / 261

Z8
®
CPU
User Manual
UM001604-0108 Interrupts
98
IRQ3 can be generated from an external source only if Serial In is not enabled. Otherwise,
its source is internal. The external request is generated by a Low edge signal on P30 as dis-
played in
Figure 93 . Again, the external request is synchronized and delayed before reach-
ing IRQ3. Some Z8 products replace P30 with P32 as the external source for IRQ3. In this
case, IRQ3 interrupt generation follows the logic as displayed in
Figure 92 on page 97.
Although interrupts are edge triggered, minimum interrupt request Low and High times
must be observed for proper operation. See the device product specification for exact tim-
ing requirements on external interrupt requests (T
W
IL, T
W
IH).
Internal Interrupt Sources
Internal sources involve interrupt requests IRQ0, IRQ2, IRQ3, IRQ4, and IRQ5. Internal
sources are ORed with the external sources, so either an internal or external source can
trigger the interrupt. Internal interrupt sources and trigger conditions are device depen-
dent.
Refer to the device product specification to determine available sources, triggering edge
options, and exact programming details. For more details on the internal interrupt sources,
see Counters and Timers, Input/Output Ports, and Serial Input/Output sections.
Interrupt Request Register Logic and Timing
Figure 94 displays the logic diagram for the Interrupt Request (IRQ) Register. The leading
edge of the request sets the first flip-flop, that remains set until interrupt requests are sam-
pled.
Requests are sampled internally during the last clock cycle before an opcode fetch (see
Figure 95 ). External requests are sampled two internal clocks earlier, due to the synchro-
nizing flip-flops as displayed in Figure 92 on page 97 and Figure 93 on page 98.
Figure 93. Interrupt Source IRQ3 Block Diagram
Note:
Q
PIN
D
Serial Receiver
P3M
6
IRQ
3
Clock
IRQ
3
IRQ
3
External Source
(IRQ
3
Serial In)
Internal Source
D
Q