Datasheet

PIC18F2220/2320/4220/4320
DS39599G-page 122 © 2007 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/CCP2 and RC0/T1OSO/T1CKI
pins become inputs. The TRISC1:TRISC0 values are
ignored and the pins read as ‘0’.
Timer1 also has an internal “Reset input”. This Reset
can be generated by the CCP module (see
Section 15.4.4 “Special Event Trigger”).
FIGURE 12-1: TIMER1 BLOCK DIAGRAM
FIGURE 12-2: TIMER1 BLOCK DIAGRAM: 16-BIT READ/WRITE MODE
T1OSC
TMR1H
TMR1L
T1SYNC
TMR1CS
T1CKPS1:T1CKPS0
Peripheral Clocks
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)
Interrupt
Flag bit
Note 1: When enable bit T1OSCEN is cleared, the inverter and feedback resistor are turned off. This eliminates power drain.
T1OSI
T1CKI/T1OSO
Timer 1
TMR1L
T1OSC
T1SYNC
TMR1CS
T1CKPS1:T1CKPS0
Peripheral Clocks
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
T1CKI/T1OSO
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