Datasheet

 1996 Microchip Technology Inc. DS30412C-page 67
PIC17C4X
11.0 TIMER0
The Timer0 module consists of a 16-bit timer/counter,
TMR0. The high byte is TMR0H and the low byte is
TMR0L. A software programmable 8-bit prescaler
makes an effective 24-bit overflow timer. The clock
source is also software programmable as either the
internal instruction clock or the RA1/T0CKI pin. The
control bits for this module are in register T0STA
(Figure 11-1).
FIGURE 11-1: T0STA REGISTER
(ADDRESS: 05h, UNBANKED)
R/W - 0 R/W - 0 R/W - 0 R/W - 0 R/W - 0 R/W - 0 R/W - 0 U - 0
INTEDG T0SE T0CS PS3 PS2 PS1 PS0
—
R = Readable bit
W = Writable bit
U = Unimplemented,
Read as '0'
-n = Value at POR reset
bit7 bit0
bit 7: INTEDG : RA0/INT Pin Interrupt Edge Select bit
This bit selects the edge upon which the interrupt is detected
1 = Rising edge of RA0/INT pin generates interrupt
0 = Falling edge of RA0/INT pin generates interrupt
bit 6: T0SE : Timer0 Clock Input Edge Select bit
This bit selects the edge upon which TMR0 will increment
When
T0CS = 0
1 = Rising edge of RA1/T0CKI pin increments TMR0 and/or generates a T0CKIF interrupt
0 = Falling edge of RA1/T0CKI pin increments TMR0 and/or generates a T0CKIF interrupt
When
T0CS = 1
Don’t care
bit 5: T0CS : Timer0 Clock Source Select bit
This bit selects the clock source for TMR0.
1 = Internal instruction clock cycle (T
CY
)
0 = T0CKI pin
bit 4-1: PS3:PS0 : Timer0 Prescale Selection bits
These bits select the prescale value for TMR0.
bit 0: Unimplemented : Read as '0'
PS3:PS0 Prescale Value
0000
0001
0010
0011
0100
0101
0110
0111
1xxx
1:1
1:2
1:4
1:8
1:16
1:32
1:64
1:128
1:256
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