Lpc2000

Firstly, thanks to all those who replied. I had 'in between times' 
switched over to using the PWM to generate the pulses and it works 
fine.

But I still couldn't understand where the jitter was coming from and 
how it was affected by seemingly un-related code changes. I will 
have a read through the document you mentioned but everything you 
say makes sense.
I just wasn't aware that this ammount of jitter could occur.

Thanks again to all.

cheers
Simon

--- In lpc2000@yahoogroups.com, "Karl Olsen" <kro@p...> wrote:
2.9 in the ARM7TDMI TRM:
> http://www.arm.com/pdfs/DDI0029G_7TDMI_R3_trm.pdf
> says that the FIQ latency is between 5 and 29 clocks.  The long 
> latencies only happen if you have slow instructions like LDM R0,
[R0-
> R15] in the main program.  Loads and stores to the Philips 
> peripherals are also relatively slow.  But still if you only have 
> NOPs and a loop branch in the main program, you must expect a 
jitter 
> of several clocks (nop = 1 clock, branch = 5 clocks if you use MAM 
> and MAMTIM=3).