An attempt of code snippet: blinkey.

After discussion and cleanup I'll post it as a FAQ.

Jan Waclawek

;Name: Blinkey
;
;What does it do: Blinks with a LED
;
;What if it does not blink: See "Basic troubleshooting FAQ"
;
;Required hardware: 
;- any '51 with reset, clock (crystal), power supply connected
;- if code in internal memory (FLASH), don't forget to connect 
;  /EA to VCC
;- one LED, cathode to port pin (see HW dependent code), 
;  anode via a series resistor (300 Ohm - 1kOhm) connected to VCC
;
;Reference assembler: asm51 from metalink webpage
;for other assemblers remove the following line
;  (causes a "duplicate definition" or similar error)
P3       EQU    0B0h

;
;
;HW dependent code
Pin      EQU    P3.0    
    ;pin, where LED is connected

Timing   EQU    4       
    ;using this value, it flashes approx. 1/sec on 12-clock '51 @ 12MHz
    ;on slightly faster hardware (e.g. 6-clocker at 20MHz)
    ;   should work, but blinks faster
    ;on significantly faster hardware, increase this value               
    ;   appropriately, as too fast blinking might seem
    ;   as if LED is continouosly ON

;code main
;ORG 0 and/or CSEG omitted for simplicity - most asms have these as default
;

X0: cpl   Pin           ;toggle LED state
    mov   r2,#Timing    ;load timing value
X1: djnz  r0,X1         ;timing done by simple nested loops
    djnz  r1,X1         ; - not precise, but good for blinkey
    djnz  r2,X1
    sjmp  X0
   
    end

The resulting "reference" hex:

:0C000000B2B07A04D8FED9FCDAFA80F421
:00000001FF