Hi Peter,

it depends only, which registers are used inside the interrupt.

And sometimes no register must be pushed, e.g. on using such instructions like INC, DEC, DJNZ, JNB, JBC, SETB, JMP, MOV, ...

Special care must be taken to the PSW register, e.g. CJNE can change it.

Following an example to increment a 16 bit value inside a timer interrupt:
<pre>
t0_int:
inc timer_b0
inc timer_b0
djnz timer_b0, t0_int1
inc timer_b1
t0_int1:
reti

Peter