Hi,

I am well screwed up on interrupts.

I have the following in my code:

SETB EXO
SETB IT0
CLR PX0 ; LOW PRIORITY

SETB EX1
SETB IT1
SETB PX1 ; HIGH PRIORITY

SETB EA

SJMP MAIN

ORG 0003H ; VECTOR FOR EX0
.........
.........
CALL EX0_ISR
.........
CLR IE0
RETI


ORG 0013H ; VECTOR FOR EX1
.........
.........
.........
CALL EX1_ISR
.........
CLR IE1
RETI


ORG 0050H

MAIN
...
...
...
...
...
.....

SJMP $ ; WAIT FOR AN INTERRUPT


EX0_ISR
.....
RET


EX1_ISR
.....
RET

<<<< PROBLEM >>>>


interrupt ex1 has higher priority.

at times ex0 stops responding and ex1 keeps working.


<<<< SOLUTION >>>>


changing ex0 and ex1 codes as below:


ORG 0003H ; VECTOR FOR EX0
CLR IE0
.........
.........
CALL EX0_ISR
.........
RETI


ORG 0013H ; VECTOR FOR EX1
CLR IE1
.........
.........
.........
CALL EX1_ISR
.........
RETI

<<<<<< >>>>>>

just by changing the line number of interrupt clearing flags from last to first, it solved the problem.



I DO NOT KNOW WHY IT SOLVED, I JUST HIT IT BY CHANCE IF IT IS THE RIGHT SOLUTION.


My book says IE0 and IE1 are cleared by automatically.


Your review and comments are appreciated please.


Simon