PIC18LF23K22-ESLASHML datasheet(162/496 Pages) MICROCHIP

162 / 496 page

PIC18(L)F2X/4XK22

DS41412C-page 162

Preliminary

 2010 Microchip Technology Inc.

12.1

Timer1/3/5 Operation

The Timer1/3/5 module is a 16-bit incrementing

counter which is accessed through the TMRxH:TMRxL

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

increments on every selected edge of the external

source.

Timer1/3/5 is enabled by configuring the TMRxON and

TMRxGE bits in the TxCON and TxGCON registers,

respectively. Table 12-1 displays the Timer1/3/5 enable

selections.

12.2

Clock Source Selection

The TMRxCS<1:0> and TxSOSCEN bits of the TxCON

Timer1/3/5. The dedicated Secondary Oscillator circuit

can be used as the clock source for Timer1, Timer3 and

Timer5, simultaneously. Any of the TxSOSCEN bits will

enable the Secondary Oscillator circuit and select it as

the clock source for that particular timer. Table 12-2

displays the clock source selections.

12.2.1

INTERNAL CLOCK SOURCE

When the internal clock source is selected the

TMRxH:TMRxL register pair will increment on multiples

of FOSC as determined by the Timer1/3/5 prescaler.

When the FOSC internal clock source is selected, the

Timer1/3/5 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

Timer1/3/5 value. To utilize the full resolution of

Timer1/3/5, an asynchronous input signal must be used

to gate the Timer1/3/5 clock input.

The following asynchronous sources may be used:

• Asynchronous event on the TxG pin to Timer1/3/5

Gate

• C1 or C2 comparator input to Timer1/3/5 Gate

12.2.2

EXTERNAL CLOCK SOURCE

When the external clock source is selected, the

Timer1/3/5 module may work as a timer or a counter.

When enabled to count, Timer1/3/5 is incremented on

the rising edge of the external clock input of the TxCKI

pin. This external clock source can be synchronized to

the microcontroller system clock or it 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 secondary internal oscillator circuit.

TABLE 12-1:

TIMER1/3/5 ENABLE

SELECTIONS

TMRxON

TMRxGE

Timer1/3/5

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:

• Timer1/3/5 enabled after POR

• Write to TMRxH or TMRxL

• Timer1/3/5 is disabled

• Timer1/3/5 is disabled (TMRxON = 0)

when TxCKI is high then Timer1/3/5

is enabled (TMRxON=1) when TxCKI

is low.

TABLE 12-2:

CLOCK SOURCE SELECTIONS

TMRxCS1

TMRxCS0

TxSOSCEN

Clock Source

System Clock (FOSC)

Instruction Clock (FOSC/4)

External Clocking on TxCKI Pin

Osc.Circuit On SOSCI/SOSCO Pins

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