PIC18F2220/2320/4220/4320
Register 12-1 details the Timer1 Control register. This
register controls the operating mode of the Timer1
module and contains the Timer1 Oscillator Enable bit
(T1OSCEN). Timer1 can be enabled or disabled by
setting or clearing control bit, TMR1ON (T1CON<0>).
12.0 TIMER1 MODULE
The Timer1 module timer/counter has the following
features:
• 16-bit timer/counter (two 8-bit registers: TMR1H
and TMR1L)
The Timer1 oscillator can be used as a secondary clock
source in power managed modes. When the T1RUN bit
is set, the Timer1 oscillator is providing the system clock.
If the Fail-Safe Clock Monitor is enabled and the Timer1
oscillator fails while providing the system clock, polling
the T1RUN bit will indicate whether the clock is being
provided by the Timer1 oscillator or another source.
• Readable and writable (both registers)
• Internal or external clock select
• Interrupt-on-overflow from FFFFh to 0000h
• Reset from CCP module special event trigger
• Status of system clock operation
Figure 12-1 is a simplified block diagram of the Timer1
module.
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.
REGISTER 12-1: T1CON: TIMER1 CONTROL REGISTER
R/W-0
RD16
R-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
T1RUN T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON
bit 0
bit 7
bit 7
bit 6
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= System clock is derived from Timer1 oscillator
0= System 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
bit 2
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(External Clock):
1= Do not synchronize external clock input
0= Synchronize external clock input
When TMR1CS = 0(Internal Clock):
This bit is ignored. Timer1 uses the internal clock when TMR1CS = 0.
bit 1
bit 0
TMR1CS: Timer1 Clock Source Select bit
1= External clock from pin RC0/T1OSO/T13CKI (on the rising edge)
0= Internal clock (FOSC/4)
TMR1ON: Timer1 On bit
1= Enables Timer1
0= Stops Timer1
Legend:
R = Readable bit
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
- n = Value at POR
2003 Microchip Technology Inc.
DS39599C-page 121
MICROCHIP [ MICROCHIP ]
