Datasheet

PIC18F6520/8520/6620/8620/6720/8720
DS39609C-page 136  2003-2013 Microchip Technology Inc.
12.1 Timer1 Operation
Timer1 can operate in one of these 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>).
When TMR1CS = 0, Timer1 increments every instruc-
tion cycle. When TMR1CS = 1, Timer1 increments on
every rising edge of the external clock input or the
Timer1 oscillator, if enabled.
When the Timer1 oscillator is enabled (T1OSCEN is
set), the RC1/T1OSI and RC0/T1OSO/T13CKI pins
become inputs. That is, the TRISC<1:0> value is
ignored and the pins are read as ‘0’.
Timer1 also has an internal “Reset input”. This
Reset can be generated by the CCP module
(see Section 16.0 “Capture/Compare/PWM (CCP)
Modules”).
FIGURE 12-1: TIMER1 BLOCK DIAGRAM
FIGURE 12-2: TIMER1 BLOCK DIAGRAM: 16-BIT READ/WRITE MODE
TMR1H
TMR1L
T1SYNC
TMR1CS
T1CKPS1:T1CKPS0
Sleep Input
F
OSC/4
Internal
Clock
TMR1ON
On/Off
Prescaler
1, 2, 4, 8
Synchronize
det
1
0
0
1
Synchronized
Clock Input
2
TMR1IF
Overflow
TMR1
CLR
CCP Special Event Trigger
T1OSCEN
Enable
Oscillator
(1)
T1OSC
Interrupt
Flag Bit
Note 1: When enable bit T1OSCEN is cleared, the inverter and feedback resistor are turned off. This eliminates power drain.
T1OSI
T1OSO/T13CKI
Timer 1
TMR1L
T1OSC
T1SYNC
TMR1CS
T1CKPS1:T1CKPS0
Sleep Input
T1OSCEN
Enable
Oscillator
(1)
TMR1IF
Overflow
Interrupt
F
OSC/4
Internal
Clock
TMR1ON
On/Off
Prescaler
1, 2, 4, 8
Synchronize
det
1
0
0
1
Synchronized
Clock Input
2
T1OSO/T13CKI
T1OSI
TMR1
Flag bit
Note 1: When enable bit T1OSCEN is cleared, the inverter and feedback resistor are turned off. This eliminates power drain.
High Byte
Data Bus<7:0>
8
TMR1H
8
8
8
Read TMR1L
Write TMR1L
CLR
CCP Special Event Trigger