ASM-PWM

ALP code for P0.0 high 10 ms and low 10 ms by using software delays.

Code Explanation

Defining the start memory location

ORG 000H

Clearing the port 0

MOV P0,#00000000B

This is a common techniq used to make sure that pins has not assigned any values or it is on low state.

Running the main function

MAIN: ACALL DELAY
      SETB P0.0
      ACALL DELAY
      CLR P0.0
      SJMP MAIN

MAIN is a lable. you can add whatever you want there.
ACALL DELAY calling the code in the lable DELAY.
SETB P0.0 setting the bit/pin 0 in port 0 high.
Keeps it high with DELAY
CLR P0.0 clearing the bit/pin by making the value 0
SJMP MAIN jump to the lable MAIN.

Software delay

DELAY:MOV R2,#10
      L1:DJNZ R2,L1
      RET 

In here I assumed the time to run DJNZ line/instruction is 1ms.

MOV R2,#10 assigning value of decimal 10 to R2.
L1:DJNZ R2,L1 Decrement the value in R2 by 1 and jump to lable L1 if the remaining value in R2 is zero. It keeps doing until the value becomes zero and the go to next instruction.

RET go to the previous location.

End of the program.

END

This simple code made on a request for 8051 micro controller and tested on a simulator. If there are any faults on the explanation please correct me.