PIC16F818-ESLASHML datasheet(59/176 Pages) MICROCHIP

59 / 176 page

 2004 Microchip Technology Inc.

DS39598E-page 57

PIC16F818/819

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 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 also be used to provide Real-Time Clock

(RTC) functionality to applications with only a minimal

addition of external components and code overhead.

7.1

Timer1 Operation

Timer1 can operate in one of three modes:

•as a timer

• as a synchronous counter

• as an asynchronous 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 the CCP1 module as the special

event trigger (see Section 9.1 “Capture Mode”).

When the Timer1 oscillator is enabled (T1OSCEN is

set), the RB6/T1OSO/T1CKI/PGC and RB7/T1OSI/

PGD pins become inputs. That is, the TRISB<7:6>

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

TMR1CS = 1:

= Do not synchronize external clock input

= 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

= External clock from pin RB6/T1OSO/T1CKI/PGC (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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