Datasheet

PIC18F2331/2431/4331/4431
DS39616D-page 132  2010 Microchip Technology Inc.
13.1 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 Timer1 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/CCP2/FLTA
and RC0/T1OSO/
T1CKI 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 16.4.4 “Special Event Trigger”).
FIGURE 13-1: TIMER1 BLOCK DIAGRAM
FIGURE 13-2: TIMER1 BLOCK DIAGRAM (16-BIT READ/WRITE MODE)
T1SYNC
TMR1CS
T1CKPS<1:0>
Sleep Input
T1OSCEN
(1)
FOSC/4
Internal
Clock
On/Off
Prescaler
1, 2, 4, 8
Synchronize
Detect
1
0
2
T1OSO/T1CKI
T1OSI
1
0
TMR1ON
TMR1L
Set
TMR1IF
on Overflow
TMR1
High Byte
Clear TMR1
(CCP Special Event Trigger)
Timer1 Oscillator
Note 1: When enable bit, T1OSCEN, is cleared, the inverter and feedback resistor are turned off to eliminate power drain.
On/Off
Timer1
Timer1 Clock Input
T1SYNC
TMR1CS
T1CKPS<1:0>
Sleep Input
T1OSCEN
(1)
FOSC/4
Internal
Clock
Prescaler
1, 2, 4, 8
Synchronize
Detect
1
0
2
T1OSO/T1CKI
T1OSI
Note 1: When enable bit, T1OSCEN, is cleared, the inverter and feedback resistor are turned off to eliminate power drain.
1
0
TMR1L
Internal Data Bus
8
Set
TMR1IF
on Overflow
TMR1
TMR1H
High Byte
8
8
8
Read TMR1L
Write TMR1L
8
TMR1ON
Clear TMR1
(CCP Special Event Trigger)
Timer1 Oscillator
On/Off
Timer1
Timer1 Clock Input