PIC16F877AISLASHML datasheet(59/234 Pages) MICROCHIP

59 / 234 page

 2003 Microchip Technology Inc.

DS39582B-page 57

PIC16F87XA

6.0

TIMER1 MODULE

The Timer1 module is a 16-bit timer/counter consisting

of two 8-bit registers (TMR1H and TMR1L) which are

readable and writable. The TMR1 register pair

(TMR1H:TMR1L) increments from 0000h to FFFFh

and rolls over to 0000h. The TMR1 interrupt, if enabled,

is generated on overflow which is latched in interrupt

flag bit, TMR1IF (PIR1<0>). This interrupt can be

enabled/disabled by setting/clearing TMR1 interrupt

enable bit, TMR1IE (PIE1<0>).

Timer1 can operate in one of two modes:

•As a Timer

• As a Counter

The operating mode is determined by the clock select

bit, TMR1CS (T1CON<1>).

In Timer mode, Timer1 increments every instruction

cycle. In Counter mode, it increments on every rising

edge of the external clock input.

Timer1 can be enabled/disabled by setting/clearing

control bit, TMR1ON (T1CON<0>).

Timer1 also has an internal “Reset input”. This Reset

can be generated by either of the two CCP modules

(Section 8.0 “Capture/Compare/PWM Modules”).

When the Timer1 oscillator is enabled (T1OSCEN is

set), the RC1/T1OSI/CCP2 and RC0/T1OSO/T1CKI

pins become inputs. That is, the TRISC<1:0> value is

ignored and these pins read as ‘0’.

Additional information on timer modules is available in

the PICmicro® Mid-Range MCU Family Reference

Manual (DS33023).

T1CON: TIMER1 CONTROL REGISTER (ADDRESS 10h)

U-0

R/W-0

—

T1CKPS1 T1CKPS0

T1OSCEN

T1SYNC TMR1CS TMR1ON

bit 7

bit 0

bit 7-6

Unimplemented: Read as ‘0’

bit 5-4

T1CKPS1:T1CKPS0: Timer1 Input Clock Prescale Select bits

= 1:8 prescale value

= 1:4 prescale value

= 1:2 prescale value

= 1:1 prescale value

bit 3

T1OSCEN: Timer1 Oscillator Enable Control bit

= Oscillator is enabled

= Oscillator is shut-off (the oscillator inverter is turned off to eliminate power drain)

bit 2

T1SYNC: Timer1 External Clock Input Synchronization Control bit

When TMR1CS = 1:

= Do not synchronize external clock input

= Synchronize external clock input

When TMR1CS = 0:

This bit is ignored. Timer1 uses the internal clock when TMR1CS = 0.

bit 1

TMR1CS: Timer1 Clock Source Select bit

= External clock from pin RC0/T1OSO/T1CKI (on the rising edge)

= Internal clock (FOSC/4)

bit 0

TMR1ON: Timer1 On bit

= Enables Timer1

= Stops Timer1

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

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