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
register (Register 12-1). 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 12-1:
R/W-0
RD16
bit 7
Legend:
R = Readable bit
-n = Value at POR
bit 7
T1CON: TIMER1 CONTROL REGISTER
R-0
R/W-0
T1CKPS1
R/W-0
T1CKPS0
R/W-0
T1OSCEN
R/W-0
T1SYNC
R/W-0
TMR1CS
R/W-0
TMR1ON
bit 0
T1RUN
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
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
T1RUN:
Timer1 System Clock Status bit
1
= Device clock is derived from Timer1 oscillator
0
= Device clock is derived from another source
T1CKPS<1:0>:
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
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.
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.
TMR1CS:
Timer1 Clock Source Select bit
1
= External clock from pin RC0/T1OSO/T13CKI (on the rising edge)
0
= Internal clock (F
OSC
/4)
TMR1ON:
Timer1 On bit
1
= Enables Timer1
0
= Stops Timer1
bit 6
bit 5-4
bit 3
bit 2
bit 1
bit 0
©
2008 Microchip Technology Inc.
DS39631E-page 127
MICROCHIP [ MICROCHIP TECHNOLOGY ]
