PWM with 89S52

Here is the program for Pulse width modulation PWM on basic for 89s52.

You could generate pwm using the following psedocode

#define high_period
#define low_period

main()
{
!!Code to initiate the timer;
!!Timer counter register value = high_period;
!!set port pin high
!!start timer
while(1);
}

interrupt void time_interrupt_routine(void)
{
if(port pin is high)
!!Timer counter register value = low_period;

else
!!Timer counter register value = high_period;

!!Toggle port pin
!! start timer;
}

Here high_period + low_period gives the time period in terms of clock cycle and

high_period/(high_period + low_period) *100 gives the dutycycle.

How to access R0 to R7 registers in Keil C?

you can use the following Program to access R0 to R7 registers in Keil C


{

unsigned char R0Val;

_asm

MOV A, R0
MOV _R0Val, A

_endasm

}

OR

{

unsigned char R0Val;

#pragma ASM

MOV A, R0
MOV _R0Val, A

#pragma ENDASM

}

C variables have to be prefixed by '_' or underscore character, to be accessible in the assembly section of the C code.

Hope this helps.