PIC18FXX20 Datasheet, PDF (138/366 Pages) Microchip Technology – 64/80-Pin High Performance 1 Mbit Enhanced FLASH Microcontrollers with A/D

PIC18FXX20
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
(Section 16.0).
FIGURE 12-1:
TIMER1 BLOCK DIAGRAM
TMR1IF
Overflow
Interrupt
Flag Bit
T13CKI/T1OSO
T1OSI
CCP Special Event Trigger
TMR1
CLR
TMR1H TMR1L
T1OSC
T1OSCEN
Enable
Oscillator⁽¹⁾
0
Synchronized
Clock Input
TMR1ON
On/Off
1
T1SYNC
FOSC/4
Internal
Clock
1
Prescaler
1, 2, 4, 8
0
2
T1CKPS1:T1CKPS0
TMR1CS
Synchronize
det
SLEEP Input
Note 1: When enable bit T1OSCEN is cleared, the inverter and feedback resistor are turned off. This eliminates power drain.
FIGURE 12-2:
TIMER1 BLOCK DIAGRAM: 16-BIT READ/WRITE MODE
Data Bus<7:0>
8
TMR1H
8
8
Write TMR1L
Read TMR1L
CCP Special Event Trigger
TMR1IF
Overflow
Interrupt
Flag bit
T13CKI/T1OSO
T1OSI
8
TMR1
Timer 1
High Byte
CLR
TMR1L
T1OSC
T1OSCEN
Enable
Oscillator⁽¹⁾
0
Synchronized
Clock Input
TMR1ON
On/Off
1
T1SYNC
1
FOSC/4
Internal
Clock
0
TMR1CS
Prescaler
1, 2, 4, 8
2
Synchronize
det
SLEEP Input
T1CKPS1:T1CKPS0
Note 1: When enable bit T1OSCEN is cleared, the inverter and feedback resistor are turned off. This eliminates power drain.
DS39609A-page 136
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