I don't yet know if my C is faulty, but the below sequence looks a little strange to me, in respect to the clearing of the variable "c", which is - as far as I can tell, used nowhere, neither in this snippet nor anywhere below it.

Or is the "c" the carry-bit?

--------------------------------------

;     while(1)
			; SOURCE LINE # 58
;     {
			; SOURCE LINE # 59
;         P1 ^= 0x10;                     // Toggles every 8th usec, 125 kHz
			; SOURCE LINE # 60
	XRL  	P1,#010H
; 
;         if(timer0_tick >= 14)           /* Timer input = OSC/12 = 921.600 kHz */
			; SOURCE LINE # 62
	MOV  	DPTR,#timer0_tick
	MOVX 	A,@DPTR
	CLR  	C
	XRL  	A,#080H
	SUBB 	A,#08EH
	JC   	?C0006
;         {                               /* => 14 overflows per second         */
			; SOURCE LINE # 63
;             secs++; 
			; SOURCE LINE # 64
	MOV  	DPTR,#secs+01H
	MOVX 	A,@DPTR
	INC  	A
	MOVX 	@DPTR,A
	JNZ  	?C0011
	MOV  	DPTR,#secs
	MOVX 	A,@DPTR
	INC  	A
	MOVX 	@DPTR,A
?C0011:

--------------------------------------

Why would we want to only continue mangling with "secs" if the accumulator is not zero? Incrementing it makes it "never zero", doesn't it? But then again - why does this piece of code try to access "secs" at an address 1 bit higher than it ought to be (#secs+01h)?

--------------------------------------

;             timer0_tick = 0; 
			; SOURCE LINE # 65
	CLR  	A
	MOV  	DPTR,#timer0_tick
	MOVX 	@DPTR,A
;             P1 ^= 0x01; 
			; SOURCE LINE # 66
	XRL  	P1,#01H
;         }
			; SOURCE LINE # 67
?C0006:

--------------------------------------

I understand the last part and it seems logical - resetting the accumulator to zero, moving the address of "timer0_tick" into a pointer and then moving the contents of the accumulator to the gathered address.

Or'ing P1 with 01 hex toggles P1.0.

/Thomas