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Semiconductor Group
122
Interrupt System
Figure 8-8
Priority-Within-Level Structure
Note:
This "priority-within-level" structure is only used to resolve simultaneous requests of the same
priority level.
8.3
How Interrupts are Handled
The interrupt flags are sampled at S5P2 in each machine cycle. The sampled flags are polled during
the following machine cycle. lf one of the flags was in a set condition at S5P2 of the preceding cycle,
the polling cycle will find it and the interrupt system will generate a LCALL to the appropriate service
routine, provided this hardware-generated LCALL is not blocked by any of the following conditions:
1)
An interrupt of equal or higher priority is already in progress.
2)
The current (polling) cycle is not in the final cycle of the instruction in progress.
3)
The instruction in progress is RETI or any write access to registers IEN0, IEN1, IEN2 or IP0
and IP1.
Any of these three conditions will block the generation of the LCALL to the interrupt service routine.
Condition 2 ensures that the instruction in progress is completed before vectoring to any service
routine. Condition 3 ensures that if the instruction in progress is RETI or any write access to
registers IEN0, IEN1 or IP0 and IP1, then at least one more instruction will be executed before any
interrupt is vectored too; this delay guarantees that changes of the interrupt status can be observed
by the CPU.
High
→
Low
Priority
Interrupt source
IE0
IADC
TF0
IEX2
IE1
IEX3
TF1
IEX4
RI + TI
IEX5
TF2 + EXF2
IEX6
High
↓
Low
*
Summary of Contents for SAB 80515 Series
Page 9: ...Semiconductor Group 9 Introduction Figure 1 2 Block Diagram ...
Page 12: ...Semiconductor Group 12 Fundamental Structure Figure 2 1 Detailed Block Diagram ...
Page 18: ...Semiconductor Group 18 Central Processing Unit Figure 3 1 Fetch Execute Sequence ...
Page 73: ...Semiconductor Group 73 On Chip Peripheral Components Figure 7 25 A D Converter Block Diagram ...
Page 83: ...Semiconductor Group 83 On Chip Peripheral Components Figure 7 33 a Timer 2 Block Diagram ...
Page 215: ...Device Specifications Semiconductor Group 215 ...
Page 217: ...Device Specifications Semiconductor Group 217 Pin Configuration P LCC 68 ...
Page 219: ...Device Specifications Semiconductor Group 219 Logic Symbol ...
Page 226: ...Device Specifications Semiconductor Group 226 Figure 1 Block Diagram ...
Page 229: ...Device Specifications Semiconductor Group 229 Figure 2 Memory Address Spaces ...
Page 239: ...Device Specifications Semiconductor Group 239 Figure 4 Block Diagram of the A D Converter ...
Page 241: ...Device Specifications Semiconductor Group 241 Figure 5 Interrupt Request Sources ...
Page 242: ...Device Specifications Semiconductor Group 242 Figure 6 Interrupt Priority Level Structure ...