PIC18F4520ESLASHMLQTP datasheet(129/390 Pages) MICROCHIP

129 / 390 page

 2004 Microchip Technology Inc.

Preliminary

DS39631A-page 127

PIC18F2420/2520/4420/4520

12.0

TIMER1 MODULE

The Timer1 timer/counter module incorporates these

features:

• Software selectable operation as a 16-bit timer or

counter

• Readable and writable 8-bit registers (TMR1H

and TMR1L)

• Selectable clock source (internal or external) with

device clock or Timer1 oscillator internal options

• Interrupt-on-overflow

• Reset on CCP Special Event Trigger

• Device clock status flag (T1RUN)

A simplified block diagram of the Timer1 module is

shown in Figure 12-1. A block diagram of the module’s

operation in Read/Write mode is shown in Figure 12-2.

The module incorporates its own low-power oscillator

to provide an additional clocking option. The Timer1

oscillator can also be used as a low-power clock source

for the microcontroller in power managed operation.

Timer1 can also be used to provide Real-Time Clock

(RTC) functionality to applications with only a minimal

addition of external components and code overhead.

Timer1 is controlled through the T1CON Control

Oscillator Enable bit (T1OSCEN). Timer1 can be

enabled or disabled by setting or clearing control bit,

TMR1ON (T1CON<0>).

T1CON: TIMER1 CONTROL REGISTER

R/W-0

R-0

R/W-0

RD16

T1RUN

T1CKPS1

T1CKPS0

T1OSCEN

T1SYNC

TMR1CS

TMR1ON

bit 7

bit 0

bit 7

RD16: 16-bit Read/Write Mode Enable bit

= Enables register read/write of TImer1 in one 16-bit operation

= Enables register read/write of Timer1 in two 8-bit operations

bit 6

T1RUN: Timer1 System Clock Status bit

= Device clock is derived from Timer1 oscillator

= Device clock is derived from another source

bit 5-4

T1CKPS1:T1CKPS0: Timer1 Input Clock Prescale Select bits

= 1:8 Prescale value

= 1:4 Prescale value

= 1:2 Prescale value

= 1:1 Prescale value

bit 3

T1OSCEN: Timer1 Oscillator Enable bit

= Timer1 oscillator is enabled

= Timer1 oscillator is shut off

The oscillator inverter and feedback resistor are turned off to eliminate power drain.

bit 2

T1SYNC: Timer1 External Clock Input Synchronization Select bit

When TMR1CS = 1:

= Do not synchronize external clock input

= Synchronize external clock input

When TMR1CS = 0:

This bit is ignored. Timer1 uses the internal clock when TMR1CS = 0.

bit 1

TMR1CS: Timer1 Clock Source Select bit

= External clock from pin RC0/T1OSO/T13CKI (on the rising edge)

= Internal clock (FOSC/4)

bit 0

TMR1ON: Timer1 On bit

= Enables Timer1

= Stops Timer1

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

PIC18F4520E/MLQTP Datasheet(PDF) 129 Page - Microchip Technology

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