PIC16C72-04SLASHSS datasheet(57/288 Pages) MICROCHIP

57 / 288 page

DS30390E-page 57

PIC16C7X

6.0

OVERVIEW OF TIMER

MODULES

The

PIC16C72,

PIC16C73/73A,

PIC16C74/74A,

PIC16C76/77 each have three timer modules.

Each module can generate an interrupt to indicate that

an event has occurred (i.e. timer overﬂow). Each of

these modules is explained in full detail in the following

sections. The timer modules are:

• Timer0 Module (Section 7.0)

• Timer1 Module (Section 8.0)

• Timer2 Module (Section 9.0)

6.1

Timer0 Overview

The Timer0 module is a simple 8-bit overﬂow counter.

The clock source can be either the internal system

clock (Fosc/4) or an external clock. When the clock

source is an external clock, the Timer0 module can be

selected to increment on either the rising or falling

edge.

The Timer0 module also has a programmable pres-

caler option. This prescaler can be assigned to either

the Timer0 module or the Watchdog Timer. Bit PSA

(OPTION<3>) assigns the prescaler, and bits PS2:PS0

(OPTION<2:0>) determine the prescaler value. Timer0

can increment at the following rates: 1:1 (when pres-

caler assigned to Watchdog timer), 1:2, 1:4, 1:8, 1:16,

1:32, 1:64, 1:128, and 1:256 (Timer0 only).

Synchronization of the external clock occurs after the

prescaler. When the prescaler is used, the external

clock frequency may be higher then the device’s fre-

quency. The maximum frequency is 50 MHz, given the

high and low time requirements of the clock.

6.2

Timer1 Overview

Timer1 is a 16-bit timer/counter. The clock source can

be either the internal system clock (Fosc/4), an external

clock, or an external crystal. Timer1 can operate as

either a timer or a counter. When operating as a

counter (external clock source), the counter can either

operate synchronized to the device or asynchronously

to the device. Asynchronous operation allows Timer1 to

operate during sleep, which is useful for applications

that require a real-time clock as well as the power sav-

ings of SLEEP mode.

Timer1 also has a prescaler option which allows

Timer1 to increment at the following rates: 1:1, 1:2, 1:4,

and 1:8. Timer1 can be used in conjunction with the

Capture/Compare/PWM module. When used with a

Applicable Devices

72 73 73A 74 74A 76 77

Applicable Devices

72 73 73A 74 74A 76 77

Applicable Devices

72 73 73A 74 74A 76 77

CCP module, Timer1 is the time-base for 16-bit Cap-

ture or the 16-bit Compare and must be synchronized

to the device.

6.3

Timer2 Overview

Timer2 is an 8-bit timer with a programmable prescaler

and postscaler, as well as an 8-bit period register

(PR2). Timer2 can be used with the CCP1 module (in

PWM mode) as well as the Baud Rate Generator for

the Synchronous Serial Port (SSP). The prescaler

option allows Timer2 to increment at the following

rates: 1:1, 1:4, 1:16.

The postscaler allows the TMR2 register to match the

period register (PR2) a programmable number of times

before generating an interrupt. The postscaler can be

programmed from 1:1 to 1:16 (inclusive).

6.4

CCP Overview

The CCP module(s) can operate in one of these three

modes: 16-bit capture, 16-bit compare, or up to 10-bit

Pulse Width Modulation (PWM).

Capture mode captures the 16-bit value of TMR1 into

the CCPRxH:CCPRxL register pair. The capture event

can be programmed for either the falling edge, rising

edge, fourth rising edge, or the sixteenth rising edge of

the CCPx pin.

Compare mode compares the TMR1H:TMR1L register

pair to the CCPRxH:CCPRxL register pair. When a

match occurs an interrupt can be generated, and the

output pin CCPx can be forced to given state (High or

Low), TMR1 can be reset (CCP1), or TMR1 reset and

start A/D conversion (CCP2). This depends on the con-

trol bits CCPxM3:CCPxM0.

PWM mode compares the TMR2 register to a 10-bit

duty cycle register (CCPRxH:CCPRxL<5:4>) as well as

to an 8-bit period register (PR2). When the TMR2 reg-

ister = Duty Cycle register, the CCPx pin will be forced

low. When TMR2 = PR2, TMR2 is cleared to 00h, an

interrupt can be generated, and the CCPx pin (if an out-

put) will be forced high.

Applicable Devices

72 73 73A 74 74A 76 77

Applicable Devices

72 73 73A 74 74A 76 77

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