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2007 Microchip Technology Inc.
DS21993C-page 43
PIC16CR7X
5.0
TIMER0 MODULE
The Timer0 module timer/counter has the following
features:
8-bit timer/counter
Readable and writable
8-bit software programmable prescaler
Internal or external clock select
Interrupt on overflow from FFh to 00h
Edge select for external clock
Additional information on the Timer0 module is
available in the “PIC Mid-Range MCU Family
Reference Manual” (DS33023).
Figure 5-1 is a block diagram of the Timer0 module and
the prescaler shared with the WDT.
Timer0
operation
is
controlled
through
the
page). Timer mode is selected by clearing bit T0CS
(OPTION_REG<5>). In Timer mode, the Timer0 mod-
ule will increment every instruction cycle (without pres-
caler). If the TMR0 register is written, the increment is
inhibited for the following two instruction cycles. The
user can work around this by writing an adjusted value
to the TMR0 register.
Counter mode is selected by setting bit T0CS
(OPTION_REG<5>). In Counter mode, Timer0 will
increment, either on every rising or falling edge of pin
RA4/T0CKI. The incrementing edge is determined by
the
Timer0
Source
Edge
Select
bit
T0SE
(OPTION_REG<4>). Clearing bit T0SE selects the ris-
ing edge. Restrictions on the external clock input are
The prescaler is mutually exclusively shared between
the Timer0 module and the Watchdog Timer. The
5.1
Timer0 Interrupt
The TMR0 interrupt is generated when the TMR0 reg-
ister overflows from FFh to 00h. This overflow sets bit
TMR0IF (INTCON<2>). The interrupt can be masked
by clearing bit TMR0IE (INTCON<5>). Bit TMR0IF
must be cleared in software by the Timer0 module
Interrupt Service Routine, before re-enabling this inter-
rupt. The TMR0 interrupt cannot awaken the processor
from Sleep, since the timer is shut-off during Sleep.
FIGURE 5-1:
BLOCK DIAGRAM OF THE TIMER0 MODULE AND PRESCALER
RA4/T0CKI
T0SE
pin
M
U
X
CLKOUT (= FOSC/4)
SYNC
2
Cycles
TMR0 Reg
8-bit Prescaler
8-to-1 MUX
M
U
X
M U X
Watchdog
Timer
PSA
0
1
0
1
WDT
Time-out
PS2:PS0
8
Note: T0CS, T0SE, PSA, PS2:PS0 are (OPTION_REG<5:0>).
PSA
WDT Enable bit
M
U
X
0
1
0
1
Data Bus
Set Flag bit TMR0IF
on Overflow
8
PSA
T0CS
PRESCALER