dear darrel

thanks for your reply

you are right about preloading timer1, i've changed two steps before from 4mhz to 20 mhz ;-)

RESUME MAIN would be fine theoretical when the interrupt routine is started only when pointer is in main loop. now it is a problem because even when the ISR is executed, the pointer jumps into main loop after.

i've changed the "resume main" to resume" only, and it work better....

but my basic problem is still here, timer1 overflows to early in the programm code (in the while-when of the pre loop). but my idea is to start timer1 not until end of pre loop. why does this appear? in my opinion only T1CON.0 = 1 starts the timer1, isn't it?

i've now solved the problem with a flag :

- clear it at begin of init
- execute ISR only when it is 1, else resume
- set flag = 1 on end of init section

so, fine would be if i could reach that with timer1

thanks for any hints again. cheers