41594B datasheet(162/372 Pages) MICROCHIP

162 / 372 page

PIC12LF1840T48A

DS41594B-page 162

Preliminary

 2011-2012 Microchip Technology Inc.

21.1

Timer1 Operation

The Timer1 module is a 16-bit incrementing counter

which is accessed through the TMR1H:TMR1L register

pair. Writes to TMR1H or TMR1L directly update the

counter.

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 and incre-

ments 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. Table 21-1 displays the Timer1 enable

selections.

21.2

Clock Source Selection

The TMR1CS<1:0> and T1OSCEN bits of the T1CON

Table 21-2 displays the clock source selections.

21.2.1

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.

When the FOSC internal clock source is selected, the

Timer1 register value will increment by four counts every

instruction clock cycle. Due to this condition, a 2 LSB

error in resolution will occur when reading the Timer1

value. To utilize the full resolution of Timer1, an

asynchronous input signal must be used to gate the

Timer1 clock input.

The following asynchronous sources may be used:

• Asynchronous event on the T1G pin to Timer1

gate

• C1 comparator input to Timer1 gate

21.2.2

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 or the

capacitive sensing oscillator signal. 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 21-1:

TIMER1 ENABLE

SELECTIONS

TMR1ON

TMR1GE

Timer1

Operation

Off

Always On

Count Enabled

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 enabled after POR

• Write to TMR1H or TMR1L

• Timer1 is disabled

• Timer1 is disabled (TMR1ON = 0)

when T1CKI is high then Timer1 is

enabled (TMR1ON=1) when T1CKI is

low.

TABLE 21-2:

CLOCK SOURCE SELECTIONS

TMR1CS1

TMR1CS0

T1OSCEN

Clock Source

System Clock (FOSC)

Instruction Clock (FOSC/4)

Capacitive Sensing Oscillator

External Clocking on T1CKI Pin

Osc.Circuit On T1OSI/T1OSO Pins

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