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PIC18F66K80 FAMILY

DS39977F-page 212

2010-2012 Microchip Technology Inc.

14.2

Timer1 Operation

The Timer1 module is an 8 or 16-bit incrementing

counter that is accessed through the TMR1H:TMR1L

When used with an internal clock source, the module is

a timer and increments on every instruction cycle.

When used with an external clock source, the module

can be used as either a timer or counter. It increments

on every selected edge of the external source.

Timer1 is enabled by configuring the TMR1ON and

TMR1GE bits in the T1CON and T1GCON registers,

respectively.

When SOSC is selected as Crystal mode (by the

SOSCSELx bits), the RC1/SOSCI and RC0/SOSCO/

SCLKI pins become inputs. This means the values of

TRISC<1:0> are ignored and the pins are read as ‘0’.

14.3

Clock Source Selection

The TMR1CS<1:0> and SOSCEN bits of the T1CON

Table 14-1 displays the clock source selections.

14.3.1

INTERNAL CLOCK SOURCE

When the internal clock source is selected, the

TMR1H:TMR1L register pair will increment on multiples

of FOSC as determined by the Timer1 prescaler.

14.3.2

EXTERNAL CLOCK SOURCE

When the external clock source is selected, the Timer1

module may work as a timer or a counter.

When enabled to count, Timer1 is incremented on the

rising edge of the external clock input, T1CKI. Either of

these external clock sources can be synchronized to the

microcontroller system clock or they can run

asynchronously.

When used as a timer with a clock oscillator, an

external, 32.768 kHz crystal can be used in conjunction

with the dedicated internal oscillator circuit.

TABLE 14-1:

TIMER1 CLOCK SOURCE SELECTION

Note:

In Counter mode, a falling edge must be

registered by the counter prior to the first

incrementing rising edge after any one or

more of the following conditions:

Timer1 is enabled after POR Reset

Write to TMR1H or TMR1L

Timer1 is disabled

Timer1 is disabled (TMR1ON = 0)

When T1CKI is high, Timer1 is enabled

(TMR1ON = 1) when T1CKI is low.

TMR1CS1

TMR1CS0

SOSCEN

Clock Source

Clock Source (FOSC)

Instruction Clock (FOSC/4)

External Clock on T1CKI Pin

Oscillator Circuit on SOSCI/SOSCO Pins

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