
2002 Microchip Technology Inc.
Preliminary
DS30485A-page 109
PIC18FXX39
13.0 TIMER3 MODULE
The Timer3 module timer/counter has the following
features:
16-bit timer/counter
(two 8-bit registers: TMR3H and TMR3L)
Readable and writable (both registers)
Internal or external clock select
Interrupt-on-overflow from FFFFh to 0000h
Figure 13-1 is a simplified block diagram of the Timer3
module.
sets the Operating mode of the Timer1 module.
REGISTER 13-1:
T3CON: TIMER3 CONTROL REGISTER
R/W-0
RD16
—
T3CKPS1 T3CKPS0
—
T3SYNC
TMR3CS TMR3ON
bit 7
bit 0
bit 7
RD16: 16-bit Read/Write Mode Enable bit
1
= Enables register read/write of Timer3 in one 16-bit operation
0
= Enables register read/write of Timer3 in two 8-bit operations
bit 6, 3
Unimplemented: Maintain as ‘0’
bit 5, 4
T3CKPS1:T3CKPS0: Timer3 Input Clock Prescale Select bits
11
= 1:8 Prescale value
10
= 1:4 Prescale value
01
= 1:2 Prescale value
00
= 1:1 Prescale value
bit 2
T3SYNC: Timer3 External Clock Input Synchronization Control bit
(Not usable if the system clock comes from Timer1/Timer3)
When TMR3CS = 1:
1
= Do not synchronize external clock input
0
= Synchronize external clock input
When TMR3CS = 0:
This bit is ignored. Timer3 uses the internal clock when TMR3CS = 0.
bit 1
TMR3CS: Timer3 Clock Source Select bit
1
= External clock input from T13CKI
(on the rising edge after the first falling edge)
0
= Internal clock (FOSC/4)
bit 0
TMR3ON: Timer3 On bit
1
= Enables Timer3
0
= Stops Timer3
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
- n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
x = Bit is unknown