understanding bit shifting

[khatus]

https://www.best-microcontroller-projects.com/pwm-pic.html


Controlling the PIC PWM output
The PIC microcontrollers are very easy to use with PWM as they have built in PWM generators - all you do is set up the relevant control registers

Code: [Select]

// Timer 2 PIC PWM
PR2=199; // 4 MHz clock -> 5kHz PWM frequency
T2CON = (1<<TMR2ON);

// Initialize Control PIC PWM
CCPR1L = 30; // Initial Duty
CCP1CON = 0x0f; // PWM mode set and 5,4 duty = 0

...and then control the duty cycle:

CCPR1L = j;

Note that the above control only controls the upper 8 bits of the 10 bit PWM module (the other two bits are in a CCP1CON).

Here how does T2CON = (1<<TMR2ON); works??

[Siwastaja]

TMR2ON is #defined elsewhere (likely in some .h file provided by Microchip), and hopefully equals to 2. This means, the compiler preprocessor replaces TMR2ON with 2.

(1<<2) means that value 1 is shifted left by two places:
0000 0001
->
0000 0010
->
0000 0100

[admiralk]

It is not a very good idea to use equality (=) to do that as it could also change all the other bits, if they are not already 0. If you are only wanting to change one bit, you should or (|=) the value. So

Code: [Select]

T2CON |= (1 << TMR2ON);

is the proper way to do it. That way you only set the TMR2ON bit and leave the rest unchanged.