
PIC18F85J11 FAMILY
DS39774D-page 166
2010 Microchip Technology Inc.
15.1
Timer3 Operation
Timer3 can operate in one of three modes:
Timer
Synchronous Counter
Asynchronous Counter
The operating mode is determined by the clock select
bit, TMR3CS (T3CON<1>). When TMR3CS is cleared
(= 0), Timer3 increments on every internal instruction
cycle (FOSC/4). When the bit is set, Timer3 increments
on every rising edge of the Timer1 external clock input
or the Timer1 oscillator, if enabled.
As
with
Timer1,
the
RC1/T1OSI
and
RC0/T1OSO/T13CKI pins become inputs when the
Timer1 oscillator is enabled. This means the values of
TRISC<1:0> are ignored and the pins are read as ‘0’.
FIGURE 15-1:
TIMER3 BLOCK DIAGRAM (8-BIT MODE)
FIGURE 15-2:
TIMER3 BLOCK DIAGRAM (16-BIT READ/WRITE MODE)
T3SYNC
TMR3CS
T3CKPS<1:0>
Sleep Input
T1OSCEN(1)
FOSC/4
Internal
Clock
Prescaler
1, 2, 4, 8
Synchronize
Detect
1
0
2
T1OSO/T13CKI
T1OSI
1
0
TMR3ON
TMR3L
Set
TMR3IF
on Overflow
TMR3
High Byte
Timer1 Oscillator
Note 1: When enable bit, T1OSCEN, is cleared, the inverter and feedback resistor are turned off to eliminate power drain.
On/Off
Timer3
CCPx Special Event Trigger
CCPx Select from T3CON<6,3>
Clear TMR3
Timer1 Clock Input
T3SYNC
TMR3CS
T3CKPS<1:0>
Sleep Input
T1OSCEN(1)
FOSC/4
Internal
Clock
Prescaler
1, 2, 4, 8
Synchronize
Detect
1
0
2
T1OSO/T13CKI
T1OSI
Note 1: When enable bit, T1OSCEN, is cleared, the inverter and feedback resistor are turned off to eliminate power drain.
1
0
TMR3L
Internal Data Bus
8
Set
TMR3IF
on Overflow
TMR3
TMR3H
High Byte
8
Read TMR3L
Write TMR3L
8
TMR3ON
CCPx Special Event Trigger
Timer1 Oscillator
On/Off
Timer3
Timer1 Clock Input
CCPx Select from T3CON<6,3>
Clear TMR3