Avoiding getting stuck in a loop

I'm writing some code for a photography application which looks for i/p A, then waits for i/p B to change state. I/P B should change within say 500msec max. My naive approach would be to just to stick the program in a FOR count = 1 to xxxx loop, check I/P B inside the loop and if it has changed jump out of the loop with a GOTO statement. Something is bugging me about this approach and it seems that there might be a better way, perhaps using an interrupt ? Any comments ? I've never programmed with interrupts before.

Also, is there an easy way of working out how many clock cycles a particular set of PBP instructions is going to take so I can calculate what to set the count to.

Thanks, Andrew

This may not find favour with the experts, but you could try this code. No interrupts :)

Code:

---

Counter  var  byte

for Counter = 1 to 500      ' 500 mS time to find inputb
  pauseus 1000                ' pause a millisecond.  You may need to trim this value
  if InputB then ProcessB
next
' .....  do code following 500mS timeout of not getting InputB
return                            ' to wherever

ProcessB:
' do whatever you want here. You could also tell after how long InputB has come by reading the value of the Counter which counts in 1mS increments
return

---

The grain here is 1mS between samples of the inputB which I guess should be overkill for a photography application if InputB is a manual push button

Quote:

---

Originally Posted by Jerson

This may not find favour with the experts, but you could try this code. No interrupts :)

---

:eek: No interrupts!

Thanks Jerson, that is pretty much what I was proposing. This is actually for the flash sync part of a laser trigger for capturing flying insects. To reduce the granularity I coded it without the PAUSEUS. Jumping out of the FOR ... TO ... loop works fine. I was just wondering what the alternatives might be.

Andrew