PIC17C752-08SLASHCL datasheet(93/328 Pages) MICROCHIP

93 / 328 page

DS30289A-page 93

PIC17C7XX

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) out-

puts 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

corresponding 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.

11.3

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

corresponding 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 mode, 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.

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