Question

For PIC16F1619, how does the TIMER0 prescalar work? If we set PS2 = 0, PS1 = 0, and PS0 = 1 in the OPTION_REG register, how often does TIMER0 generate an interrupt?

Answer 1

Following is the block diagram of TIMER0

In above diagram we can see that prescalar can be sourced by two clock sources

1) F_OSC/4

2) T0CKI pin

• Clock source for prescalar can be selected by TMR0CS bit in OPTION_REG.
• Prescalar devides frequency of clock source by some value (power of 2).
• Internally it is some kind of frequency devider (e.g. T-Flip Flop).
• Prescalar can be bypassed by PSA bit in OPTION_REG.

Table for prescalar value and PS[2:0] bits.

PS[2:0]	Prescalar
000	2
001	4
010	8
011	16
100	32
101	64
110	128
111	256

given that

PS[2:0]=001

So from table prescalar value is 4.

Now Prescalar output frequency will depend on input frequency

Now say fosc=16MHz and Prescalar is 4

Interrupt can either be generated by INT pin or timer overflow.

Timer overflow interrupt is generated when overflow occurs on timer.

Timer overflow Interrupt enabled by setting up INTCON Register (if required set it up).

Time delay for timer overflow interrupt can be calculated as follows

for 16Mhz frequency and 001 PS[2:0] bits.