16F628 datasheet(50/168 Pages) MICROCHIP

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PIC16F627A/628A/648A

DS40044A-page 48

Preliminary

 2002 Microchip Technology Inc.

7.0

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 Timer1 Interrupt, if

enabled, is generated on overflow of the TMR1 register

pair which latches the interrupt flag bit TMR1IF

(PIR1<0>). This interrupt can be enabled/disabled by

setting/clearing the Timer1 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, the TMR1 register pair value incre-

ments 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 the CCP module

(Section 9.0). Register 7-1 shows the Timer1 control

For the PIC16F627A/628A/648A, when the Timer1

oscillator is enabled (T1OSCEN is set), the RB7/T1OSI

and RB6/T1OSO/T1CKI pins become inputs. That is,

the TRISB<7:6> value is ignored.

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

11 = 1:8 Prescale value

10 = 1:4 Prescale value

01 = 1:2 Prescale value

00 = 1:1 Prescale value

bit 3

T1OSCEN: Timer1 Oscillator Enable Control bit

1 = Oscillator is enabled

0 = Oscillator is shut off(1)

bit 2

T1SYNC: Timer1 External Clock Input Synchronization Control bit

TMR1CS = 1

1 = Do not synchronize external clock input

0 = Synchronize external clock input

TMR1CS = 0

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

bit 1

TMR1CS: Timer1 Clock Source Select bit

1 = External clock from pin RB6/T1OSO/T1CKI (on the rising edge)

0 = Internal clock (FOSC/4)

bit 0

TMR1ON: Timer1 On bit

1 = Disables Timer1

0 = Stops Timer1

Note 1: The oscillator inverter and feedback resistor are turned off to eliminate power drain.

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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