Datasheet

 1997 Microchip Technology Inc. DS30444E - page 51
PIC16C9XX
8.0 TIMER1 MODULE
Timer1 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 operate in one of two modes:
• As a timer
• As a 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 turned on and off using the control bit
TMR1ON (T1CON<0>).
Timer1 also has an internal “reset input”. This reset can
be generated by the CCP module (Section 10.0).
Figure 8-1 shows the Timer1 control register.
When the Timer1 oscillator is enabled (T1OSCEN is
set), the RC1/T1OSI and RC0/T1OSO/T1CKI pins
become inputs.
FIGURE 8-1: 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 R = Readable bit
W = Writable bit
U = Unimplemented bit,
read as ‘0’
- n = Value at POR reset
bit7 bit0
bit 7-6: Unimplemented: Read as '0'
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: T1OSCEN: Timer1 Oscillator Enable Control bit
1 = Oscillator is enabled
0 = Oscillator is shut off
Note: The oscillator inverter and feedback resistor are turned off to eliminate power drain
bit 2: 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: TMR1CS: Timer1 Clock Source Select bit
1 = External clock from pin T1CKI (on the rising edge)
0 = Internal clock (Fosc/4)
bit 0: TMR1ON: Timer1 On bit
1 = Enables Timer1
0 = Stops Timer1