PIC18F23K20-ESLASHML datasheet(167/456 Pages) MICROCHIP

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DS41303G-page 167

PIC18F2XK20/4XK20

14.0

TIMER2 MODULE

The Timer2 module timer incorporates the following

features:

• 8-bit timer and period registers (TMR2 and PR2,

respectively)

• Readable and writable (both registers)

• Software programmable prescaler (1:1, 1:4 and

1:16)

• Software programmable postscaler (1:1 through

1:16)

• Interrupt on TMR2-to-PR2 match

• Optional use as the shift clock for the MSSP

module

The module is controlled through the T2CON register

(Register 14-1), which enables or disables the timer

and configures the prescaler and postscaler. Timer2

can be shut off by clearing control bit, TMR2ON of the

T2CON register, to minimize power consumption.

A simplified block diagram of the module is shown in

Figure 14-1.

14.1

Timer2 Operation

In normal operation, TMR2 is incremented from 00h on

each clock (FOSC/4). A 4-bit counter/prescaler on the

clock

input

gives

direct

input,

divide-by-4

and

divide-by-16 prescale options; these are selected by

the prescaler control bits, T2CKPS<1:0> of the T2CON

period register, PR2, on each clock cycle. When the

two values match, the comparator generates a match

signal as the timer output. This signal also resets the

value of TMR2 to 00h on the next cycle and drives the

output counter/postscaler (see Section 14.2 “Timer2

Interrupt”).

The TMR2 and PR2 registers are both directly readable

and writable. The TMR2 register is cleared on any

device Reset, whereas the PR2 register initializes to

FFh. Both the prescaler and postscaler counters are

cleared on the following events:

• a write to the TMR2 register

• a write to the T2CON register

• any device Reset (Power-on Reset, MCLR Reset,

Watchdog Timer Reset or Brown-out Reset)

TMR2 is not cleared when T2CON is written.

T2CON: TIMER2 CONTROL REGISTER

U-0

R/W-0

—

T2OUTPS3

T2OUTPS2

T2OUTPS1

T2OUTPS0

TMR2ON

T2CKPS1

T2CKPS0

bit 7

bit 0

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

bit 7

Unimplemented: Read as ‘0’

bit 6-3

T2OUTPS<3:0>: Timer2 Output Postscale Select bits

0000

= 1:1 Postscale

0001

= 1:2 Postscale

•

1111

= 1:16 Postscale

bit 2

TMR2ON: Timer2 On bit

= Timer2 is on

= Timer2 is off

bit 1-0

T2CKPS<1:0>: Timer2 Clock Prescale Select bits

= Prescaler is 1

= Prescaler is 4

= Prescaler is 16

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