interrupt 20x2

[ColinP]

Hi – I have a problem with using interrupts on the 20x2 – I am not sure what I am doing wrong. I have a simple vehicle with a line detector which must stop when it trundles over a white line ( this produces a high to low transition on the detector output). I use the normal ‘standard’ line detector module which works fine and an L293D motor control chip which also works fine. The detector is on C.3 – the following code works -

high b.7,b.5 ; set motors forwards
low b.4,b.6

loop1:
if pinc.3=0 then stopit ; triggered by detector running over the white line
goto loop1

stopit:
low b.4,b.5,b.6,b.7 ; motors off
serout b.2,n2400,("triggered") ; message on LCD

putting c.3 onto an interrupt – the motors never turn on - no message on LCD

setint %00000000,%00001000,c
high b.7,b.5
low b.4,b.6

interrupt:
low b.4,b.5,b.6,b.7
goto loop1
return

loop1:
serout b.2,n2400,("triggered")
goto loop1

Putting the forward motor control instructions into a loop works! The buggy goes forwards and the interrupt triggers a stop and the message on the LCD

setint %00000000,%00001000,c

loop1:
high b.7,b.5
low b.4,b.6
goto loop1

interrupt:
low b.4,b.5,b.6,b.7
goto loop2
return

loop2:
serout b.2,n2400,("triggered")
goto loop2

I am not sure why this happens - I am probably missing something pretty basic any help gratefully appreciated.

Colin

 

[hippy]

setint %00000000,%00001000,c
high b.7,b.5
low b.4,b.6

interrupt:
low b.4,b.5,b.6,b.7

The program falls through initialisation straight into interrupt so the motors are turned on but only for a short period, then turned off again.

That's why adding putting a GOTO after the HIGH/LOW commands work while this doesn't.

 

[srnet]

Well unless you let the call to the Interrupt routine see the matching return, the processors going to run out of stack space at some point, I presume.