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2009 Microchip Technology Inc.

DS39636D-page 125

PIC18F2X1X/4X1X

12.0 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 12-1), which enables or disables the timer

and configures the prescaler and postscaler. Timer2

can be shut off by clearing control bit, TMR2ON

(T2CON<2>), to minimize power consumption.

A simplified block diagram of the module is shown in

Figure 12-1.

12.1

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, T2CKPS1:T2CKPS0 (T2CON<1:0>). The

value of TMR2 is compared to that of the 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 12.2 “Timer2 Interrupt”).

The TMR2 and PR2 registers are both directly readable

and writable. The TMR2 register is cleared on any

device Reset, while the PR2 register initializes at 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.

REGISTER 12-1:

T2CON: TIMER2 CONTROL REGISTER

U-0

R/W-0

—

T2OUTPS3 T2OUTPS2 T2OUTPS1 T2OUTPS0 TMR2ON T2CKPS1 T2CKPS0

bit 7

bit 0

bit 7

Unimplemented: Read as ‘0’

bit 6-3

T2OUTPS3:T2OUTPS0: Timer2 Output Postscale Select bits

0000 = 1:1 Postscale

0001 = 1:2 Postscale

1111 = 1:16 Postscale

bit 2

TMR2ON: Timer2 On bit

1 = Timer2 is on

0 = Timer2 is off

bit 1-0

T2CKPS1:T2CKPS0: Timer2 Clock Prescale Select bits

00 = Prescaler is 1

01 = Prescaler is 4

1x = Prescaler is 16

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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