PIC16F818/819
7.0
TIMER1 MODULE
The operating mode is determined by the clock select
bit, TMR1CS (T1CON<1>).
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
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’.
Additional information on timer modules is available in
the
“PICmicro
®
Mid-Range MCU Family Reference
Manual”
(DS33023).
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>).
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.
7.1
Timer1 Operation
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
—
bit 7
U-0
—
R/W-0
T1CKPS1
R/W-0
T1CKPS0
R/W-0
T1OSCEN
R/W-0
R/W-0
R/W-0
bit 0
T1SYNC TMR1CS TMR1ON
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
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.
TMR1CS:
Timer1 Clock Source Select bit
1
= External clock from pin RB6/T1OSO/T1CKI/PGC (on the rising edge)
0
= Internal clock (F
OSC
/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
bit 3
bit 2
bit 1
bit 0
2004 Microchip Technology Inc.
DS39598E-page 57
MICROCHIP [ MICROCHIP TECHNOLOGY ]
