PIC16F818/819
The operating mode is determined by the clock select
bit, TMR1CS (T1CON<1>).
7.0
TIMER1 MODULE
The Timer1 module is a 16-bit timer/counter consisting
of two 8-bit registers (TMR1H and TMR1L) which are
readable and writable. The TMR1 register pair
(TMR1H:TMR1L) increments from 0000h to FFFFh
and rolls over to 0000h. The TMR1 interrupt, if enabled,
is generated on overflow which is latched in interrupt
flag bit, TMR1IF (PIR1<0>). This interrupt can be
enabled/disabled by setting/clearing TMR1 Interrupt
Enable bit, TMR1IE (PIE1<0>).
In Timer mode, Timer1 increments every instruction
cycle. In Counter mode, it increments on every rising
edge of the external clock input.
Timer1 can be enabled/disabled by setting/clearing
control bit, TMR1ON (T1CON<0>).
Timer1 also has an internal “Reset input”. This Reset
can be generated by the CCP1 module as the special
event trigger (see Section 9.1 “Capture Mode”).
Register 7-1 shows the Timer1 Control register.
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.
When the Timer1 oscillator is enabled (T1OSCEN is
set), the RB6/T1OSO/T1CKI/PGC and RB7/T1OSI/
PGD pins become inputs. That is, the TRISB<7:6>
value is ignored and these pins read as ‘0’.
7.1
Timer1 Operation
Additional information on timer modules is available in
the “PICmicro® Mid-Range MCU Family Reference
Manual” (DS33023).
Timer1 can operate in one of three modes:
• as a timer
• as a synchronous counter
• as an asynchronous counter
REGISTER 7-1:
T1CON: TIMER1 CONTROL REGISTER (ADDRESS 10h)
U-0
—
U-0
—
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON
bit 0
bit 7
bit 7-6
bit 5-4
Unimplemented: Read as ‘0’
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 Control bit
1= Oscillator is enabled
0= Oscillator is shut-off (the oscillator inverter is turned off to eliminate power drain)
T1SYNC: Timer1 External Clock Input Synchronization Control bit
TMR1CS = 1:
1= Do not synchronize external clock input
0= Synchronize external clock input
TMR1CS = 0:
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 RB6/T1OSO/T1CKI/PGC (on the rising edge)
0= Internal clock (FOSC/4)
TMR1ON: Timer1 On bit
1= Enables Timer1
0= Stops Timer1
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
2004 Microchip Technology Inc.
DS39598E-page 57
MICROCHIP [ MICROCHIP ]
