Dear all,
here my schematic



My program

INIT:
MOV SP,#7
LOOP:
CPL P1.7
LCALL DELAY
LJMP LOOP

DELAY:
MOV R0,#1
L21:
MOV R1,#80
L11:
MOV R2,#0FFH
DJNZ R2,$
DJNZ R1,L11
DJNZ R0,L21
RET

.END

Sorry my circuit maybe not perfect, but my strong question is not in my circuit.
After I apply the power supply, Program running properly. The LED blinking constant (time on = time off).
I disturb my circuit by pressing SW1 many times, and I see the LED time blinking not constant.
My question: How the value in register R0, R1, R2 are change? If I see the delay time on the LED is like more
than 5 in the R0 in the delay subrutin but in my program I never load value more than 1 in R0.
thankyou verymuch

regard

hendry