why

Save This Code

#pragma asm
	xch	a, pulse_l		; save A
	clr	a
	xch	a, th0			; read and clear
	mov	period_l, a
	clr	a
	xch	a, tl0			; read and clear
	xch	a, pulse_l
#pragma endasm

it does not make any sense
1) It think you are trying to achieve
pulse_l - TL0;
pulse_h - TH0;
or
period_l - TL0;
period_h - TH0;
which are perfectly legit C statements

Also, you are reading a counter while it is running, a very bad idea.

Erik