Tutorial
Microcontroller 8051 |
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5.1. Interrupt The 80C51 provides 5 interrupt
sources. These are shown in Figure 17. The External Interrupts INT0
and INT1 can each be either level-activated or transition-activated,
depending on bits IT0 and IT1 in Register TCON. The flags that actually
generate these interrupts are bits IE0 and IE1 in TCON. When an external
interrupt is generated, the flag that generated it is cleared by the
hardware when the service routine is vectored to only if the interrupt
was transition-activated. If the interrupt was level-activated, then
the external requesting source is what controls the request flag, rather
than the on-chip hardware. All of the bits that generate interrupts can be set or cleared by software, with the same result as though it had been set or cleared by hardware. That is, interrupts can be generated or pending interrupts can be canceled in software. Each of these interrupt sources can be individually enabled or disabled by setting or clearing a bit in Special Function Register IE (Figure 18). IE also contains a global disable bit, EA, which disables all interrupts at once. Priority Level Structure Register IP (Figure 19). A low-priority interrupt can itself be interrupted by a high-priority interrupt, but not by another low-priority interrupt. A high-priority interrupt can’t be interrupted by any other interrupt source. If two request of different
priority levels are received simultaneously, the request of higher priority
level is serviced. If requests of the same priority level are received
simultaneously, an internal polling sequence determines which request
is serviced. Thus within each priority level there is a second priority
structure determined by the polling sequence as follows: Note that the “priority
within level” structure is only used to resolve simultaneous requests
of the same priority level. The IP register contains a number of unimplemented
bits. IP.7, IP.6, and IP.5 are reserved in the 80C51. User software
should not write 1s to these positions, since they may be used in other
8051 Family products.
Interrupt Priority Register ( IP )
Note:
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Lesson 1: Lesson 2: |
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