Generation of PWM (Pulse Width Modulation) using MC 8051

Generation of PWM (Pulse Width Modulation) using MC 8051

Calculation of timer delay generation for 8051:

TMOD Reg:

D7	D6	D5	D4	D3	D2	D1	D0
Gate	C/T	M1	M0	Gate	C/T	M1	M0

For enable timer0

We use D3-D0 bit

Gate = 0, means the Timer0 is control by software method

C/T(counter/Timer) = 0,Means Timer is Enable

M1  M0    for mode selection

0          0          Mode0: 13 bit timer

0          1          Mode1: 16bit timer

1          0          Mode2: 8bit auto reload timer

1          1          Mode3: Split timer mode

We are using mode 1

So M1 M0 = 01

D3 = 0; D2 = 0; D1 = 0; D0 = 1; rest all bit are don’t care

TMOD = 0x01;

For count calculation we must know the XTAL value in my case its 11.0592MHz

If we need time delay =1ms, that mean Required delay (Td) = 1ms;

Now we have to find Fin

Fin = XTAL/12           [12 it the total machine cycle]

Fin = (11. 0592x10^6)/12;  Fin=09216x10^6;

Tin = 1/(Fin);             Tin = 1.08506x10^-6;

Count(xx)_d = Td/Tin;          count= (1x10^-3)/(1.0856x10^-6);

Count = 921; equalent hex value = 399

(YY)_h   =     Max Count     -     Count(xx)_d;          16 bit timer max count = FFFF

(YY)_h     =     FFFF      -           399  = FC67;

This value (YY)_h  is loaded in TH0 and TL0 register in program.

For video of above program: Click for Video