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Atmel AT89C51ID2 Data Sheet - Keil

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Interrupt System The <strong>AT89C51ID2</strong> has a total of 10 interrupt vectors: two external interrupts (INT0 and<br />

INT1), three timer interrupts (timers 0, 1 and 2), the serial port interrupt, SPI interrupt,<br />

Keyboard interrupt and the PCA global interrupt. These interrupts are shown in Figure<br />

26.<br />

Figure 26. Interrupt Control System<br />

INT0<br />

TF0<br />

INT1<br />

TF1<br />

PCA IT<br />

RI<br />

TI<br />

TF2<br />

EXF2<br />

KBD IT<br />

TWI IT<br />

SPI IT<br />

Individual Enable<br />

64 <strong>AT89C51ID2</strong><br />

IE0<br />

IE1<br />

IPH, IPL<br />

3<br />

0<br />

3<br />

0<br />

3<br />

0<br />

3<br />

0<br />

3<br />

0<br />

3<br />

0<br />

3<br />

0<br />

3<br />

0<br />

3<br />

0<br />

3<br />

0<br />

Global Disable<br />

High priority<br />

interrupt<br />

Interrupt<br />

polling<br />

sequence, decreasing from<br />

high to low priority<br />

Low priority<br />

interrupt<br />

Each of the interrupt sources can be individually enabled or disabled by setting or clearing<br />

a bit in the Interrupt Enable register (Table 51 and Table 49). This register also<br />

contains a global disable bit, which must be cleared to disable all interrupts at once.<br />

Each interrupt source can also be individually programmed to one out of four priority levels<br />

by setting or clearing a bit in the Interrupt Priority register (Table 52) and in the<br />

Interrupt Priority High register (Table 50 and Table 51) shows the bit values and priority<br />

levels associated with each combination.<br />

4289A–8051–09/03

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