8-3
INTERRUPT CONTROL UNIT
8.2.1.1
Interrupt Masking
There are circumstances in which a programmer may need to disable an interrupt source tempo-
rarily (for example, while executing a time-critical section of code or servicing a high-priority
task). This temporary disabling is called interrupt masking. All interrupts from the Interrupt Con-
trol Unit can be masked either globally or individually.
The Interrupt Enable bit in the Processor Status Word globally enables or disables the maskable
interrupt request from the Interrupt Control Unit. The programmer controls the Interrupt Enable
bit with the STI (set interrupt) and CLI (clear interrupt) instructions.
Besides being globally enabled or disabled by the Interrupt Enable bit, each interrupt source can
be individually enabled or disabled. The Interrupt Mask register has a single bit for each interrupt
source. The programming can selectively mask (disable) or unmask (enable) each interrupt
source by setting or clearing the corresponding bit in the Interrupt Mask register.
8.2.1.2
Interrupt Priority
One critical function of the Interrupt Control Unit is to prioritize interrupt requests. When multi-
ple interrupts are pending, priority determines which interrupt request is serviced first. In many
systems, an interrupt handler may itself be interrupted by another interrupt source. This is known
as interrupt nesting. With interrupt nesting, priority determines whether an interrupt source can
preempt an interrupt handler that is currently executing.
Each interrupt source is assigned a priority between zero (highest) and seven (lowest). After reset,
the interrupts default to the priorities shown in Table 8-1. Because the timers share an interrupt
source, they also share a priority. Within the assigned priority, each has a relative priority (Timer
0 has the highest relative priority and Timer 2 has the lowest).
Table 8-1. Default Interrupt Priorities
Interrupt Name
Relative Priority
Timer 0
0 (a)
Timer 1
0 (b)
Timer 2
0 (c)
DMA0
1
DMA1
2
INT0
3
INT1
4
INT2
5
INT3
6
Содержание 80C186XL
Страница 1: ...80C186XL 80C188XL Microprocessor User s Manual...
Страница 2: ...80C186XL 80C188XL Microprocessor User s Manual 1995...
Страница 18: ...1 Introduction...
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Страница 27: ......
Страница 28: ...2 Overview of the 80C186 Family Architecture...
Страница 29: ......
Страница 79: ......
Страница 80: ...3 Bus Interface Unit...
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Страница 128: ...4 Peripheral Control Block...
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Страница 138: ...5 ClockGenerationand Power Management...
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Страница 154: ...6 Chip Select Unit...
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Страница 178: ...7 Refresh Control Unit...
Страница 179: ......
Страница 193: ......
Страница 194: ...8 Interrupt Control Unit...
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Страница 228: ...9 Timer Counter Unit...
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Страница 254: ...10 Direct Memory Access Unit...
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Страница 284: ...11 Math Coprocessing...
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Страница 302: ...12 ONCE Mode...
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Страница 306: ...A 80C186 Instruction Set Additions and Extensions...
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Страница 318: ...B Input Synchronization...
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Страница 322: ...C Instruction Set Descriptions...
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Страница 372: ...D Instruction Set Opcodes and Clock Cycles...
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Страница 396: ...Index...
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