PIC16F87-E Datasheet, PDF (73/228 Pages) Microchip Technology – 18/20/28-Pin Enhan lashMicrocontrollers with nanoWatt Technology

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>).
The Timer1 oscillator can be used as a secondary clock
source in low-power modes. When the T1RUN bit is set
along with SCS<1:0> = 01, the Timer1 oscillator is pro-
viding 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.
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.
PIC16F87/88
7.1 Timer1 Operation
Timer1 can operate in one of three modes:
• as a Timer
• as a Synchronous Counter
• as an Asynchronous Counter
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 Section 9.1 “Capture Mode”).
Register 7-1 shows the Timer1 Control register.
When the Timer1 oscillator is enabled (T1OSCEN is
set), the RB6/PGC/T1OSO/T1CKI and RB7/PGD/
T1OSI 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).
 2005 Microchip Technology Inc.
DS30487C-page 71