Zilog Z08470 - Manual (Page 329)

Z80 CPU Peripherals
User Manual
UM008101-0601 Serial Input/Output
309
executed or a RETI command is written to the Z80 SIO, resetting the
interrupt-under-service latch of the Channel A interrupt. At this time, the
service routine for Channel B is resumed. When the service routine is
completed, another RETI instruction is executed to complete the interrupt
service.
Figure 132. Typical Interrupt Service
IEI
High
+
High
5. Channel B Transmitter Service Routine Complete, Second RETI Issued.
Channel A
Receiver
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO
Service Completed
IEI
High
+
High
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO
IEI
High
+
Low
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI IEO
Service Resumed
Low
4. Channel A External/Status Routine Complete, RETI Issued, Channel B Transmitter Service Resumed.
IEI
High
+
Low
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI IEO
Service Suspended
Low
IEI
High
+
Low
IEO
IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI
High
IEO IEI IEO
Under Service
Low
Channel A
Transmitter
Channel A
External Status
Channel B
Receiver
Channel B
Transmitter
Channel B
External Status
3. External/Status Channel A Interrupts Suspending Service of Channel B Transmitter.
2. Channel B Transmitter Interrupts and is Acknowledged.
1. Priority Interrupt Daisy Chain before Any Interrupt Occurs.