PIC17C7XX_13 Datasheet, PDF (95/306 Pages) Microchip Technology – High-Performance 8-bit CMOS EPROM Microcontrollers with 10-bit A/D

11.0 OVERVIEW OF TIMER
RESOURCES
The PIC17C7XX has four timer modules. Each module
can generate an interrupt to indicate that an event has
occurred. These timers are called:
• Timer0 - 16-bit timer with programmable 8-bit
prescaler
• Timer1 - 8-bit timer
• Timer2 - 8-bit timer
• Timer3 - 16-bit timer
For enhanced time base functionality, four input Cap-
tures and three Pulse Width Modulation (PWM) outputs
are possible. The PWMs use the Timer1 and Timer2
resources and the input Captures use the Timer3
resource.
11.1 Timer0 Overview
The Timer0 module is a simple 16-bit overflow counter.
The clock source can be either the internal system
clock (Fosc/4) or an external clock.
When Timer0 uses an external clock source, it has the
flexibility to allow user selection of the incrementing
edge, rising or falling.
The Timer0 module also has a programmable pres-
caler. The T0PS3:T0PS0 bits (T0STA<4:1>) determine
the prescale value. TMR0 can increment at the follow-
ing rates: 1:1, 1:2, 1:4, 1:8, 1:16, 1:32, 1:64, 1:128,
1:256.
Synchronization of the external clock occurs after the
prescaler. When the prescaler is used, the external
clock frequency may be higher than the device’s fre-
quency. The maximum external frequency on the
T0CKI pin is 50 MHz, given the high and low time
requirements of the clock.
11.2 Timer1 Overview
The Timer1 module is an 8-bit timer/counter with an 8-
bit period register (PR1). When the TMR1 value rolls
over from the period match value to 0h, the TMR1IF
flag is set and an interrupt will be generated if enabled.
In Counter mode, the clock comes from the RB4/
TCLK12 pin, which can also be selected to be the clock
for the Timer2 module.
TMR1 can be concatenated with TMR2 to form a 16-bit
timer. The TMR1 register is the LSB and TMR2 is the
MSB. When in the 16-bit timer mode, there is a corre-
sponding 16-bit period register (PR2:PR1). When the
TMR2:TMR1 value rolls over from the period match
value to 0h, the TMR1IF flag is set and an interrupt will
be generated, if enabled.
PIC17C7XX
11.3 Timer2 Overview
The Timer2 module is an 8-bit timer/counter with an 8-
bit period register (PR2). When the TMR2 value rolls
over from the period match value to 0h, the TMR2IF
flag is set and an interrupt will be generated, if enabled.
In Counter mode, the clock comes from the RB4/
TCLK12 pin, which can also provide the clock for the
Timer1 module.
TMR2 can be concatenated with TMR1 to form a 16-bit
timer. The TMR2 register is the MSB and TMR1 is the
LSB. When in the 16-bit timer mode, there is a corre-
sponding 16-bit period register (PR2:PR1). When the
TMR2:TMR1 value rolls over from the period match
value to 0h, the TMR1IF flag is set and an interrupt will
be generated, if enabled.
11.4 Timer3 Overview
The Timer3 module is a 16-bit timer/counter with a 16-
bit period register. When the TMR3H:TMR3L value
rolls over to 0h, the TMR3IF bit is set and an interrupt
will be generated, if enabled. In Counter mode, the
clock comes from the RB5/TCLK3 pin.
When operating in the four Capture modes, the period
registers become the second (of four) 16-bit capture
registers.
11.5 Role of the Timer/Counters
The timer modules are general purpose, but have ded-
icated resources associated with them. TImer1 and
Timer2 are the time bases for the three Pulse Width
Modulation (PWM) outputs, while Timer3 is the time
base for the four input captures.
 1998-2013 Microchip Technology Inc.
DS30289C-page 95