• Have a good sleep
  
• Tell it to the teddy bear
  
  

• If your hypothesis is correct, you have identified the problem, and can then work on fixing it;
  
• If your hypothesis is not correct, you need to form another - maybe re-check your Observations
  

• state what is your hardware (including the exact type of the microcontroller)
  
• present only the shortest version of program which exhibits the problem (leave out irrelevant parts); but give complete program, so that other participants can verify it by compliling/assembling
  
• present a thoroughtly commented program (see the FAQ for proper commenting)
  
• state, what is the expected behaviour, and what is the reality
  
• consider attaching the resulting hex/binary file
  

• make sure your hardware works
  
  • check the power - check directly on the appropriate pins, if you have actually connected both GND and VCC
    
  • check the clock (using oscilloscope or counter)
    
  • check the reset - especially RC resets are known to produce "funny" and unpredictible results, so use a proper reset IC
    
• check the "executable" is in the code memory: read it back or verify
  
• check you really assembled/compiled those source files you intended; and you "burned" really the file which resulted from that assembling/compilation
  
• try some rudimentary "known good" code snippet
  

;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

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:00000001FF