PIC18F2450/4450
2006 Microchip Technology Inc.
Advance Information
DS39760A-page 115
11.0
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
Module Reset on CCP Special Event Trigger
Device clock status flag (T1RUN)
A simplified block diagram of the Timer1 module is
shown in Figure 11-1. A block diagram of the module’s
operation in Read/Write mode is shown in Figure 11-2.
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
register (Register 11-1). It also contains the Timer1
Oscillator Enable bit (T1OSCEN). Timer1 can be
enabled or disabled by setting or clearing control bit,
TMR1ON (T1CON<0>).
REGISTER 11-1:
T1CON: TIMER1 CONTROL REGISTER
R/W-0
R-0
R/W-0
RD16
T1RUN
T1CKPS1
T1CKPS0
T1OSCEN
T1SYNC
TMR1CS
TMR1ON
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
RD16: 16-Bit Read/Write Mode Enable bit
1
= Enables register read/write of Timer1 in one 16-bit operation
0
= Enables register read/write of Timer1 in two 8-bit operations
bit 6
T1RUN: Timer1 System Clock Status bit
1
= Device clock is derived from Timer1 oscillator
0
= Device clock is derived from another source
bit 5-4
T1CKPS1:T1CKPS0: Timer1 Input Clock Prescale Select bits
11
= 1:8 Prescale value
10
= 1:4 Prescale value
01
= 1:2 Prescale value
00
= 1:1 Prescale value
bit 3
T1OSCEN: Timer1 Oscillator Enable bit
1
= Timer1 oscillator is enabled
0
= 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:
1
= Do not synchronize external clock input
0
= 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
1
= External clock from RC0/T1OSO/T1CKI pin (on the rising edge)
0
= Internal clock (FOSC/4)
bit 0
TMR1ON: Timer1 On bit
1
= Enables Timer1
0
= Stops Timer1
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