W79E548 Datasheet, PDF (39/79 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E548/W79L548
Priority Level Structure
There are three priority levels for the interrupts, highest, high and low. The interrupt sources can be
individually set to either high or low levels. Naturally, a higher priority interrupt cannot be interrupted by
a lower priority interrupt. However there exists a pre-defined hierarchy amongst the interrupts
themselves. This hierarchy comes into play when the interrupt controller has to resolve simultaneous
requests having the same priority level. This hierarchy is defined as shown below; the interrupts are
numbered starting from the highest priority to the lowest.
Table 7. Priority structure of interrupts
SOURCE
FLAG
External Interrupt 0
IE0
Timer 0 Overflow
TF0
External Interrupt 1
IE1
Timer 1 Overflow
TF1
Serial Port
RI + TI
Timer 2 Overflow
TF2 + EXF2
Watchdog Timer
WDIF
VECTOR ADDRESS
0003h
000Bh
0013h
001Bh
0023h
002Bh
0063h
PRIORITY LEVEL
1(highest)
2
3
4
5
6
7 (lowest)
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Publication Release Date: December 12, 2005
Revision A1