PIC18F6585/8585/6680/8680
DS30491C-page 164
2004 Microchip Technology Inc.
14.0
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
Reset from CCP module trigger
Figure 14-1 is a simplified block diagram of the Timer3
module.
register controls the operating mode of the Timer3
module and sets the Enhanced CCP1 and CCP2 clock
source.
register controls the operating mode of the Timer1
module, as well as containing the Timer1 oscillator
enable bit (T1OSCEN) which can be a clock source for
Timer3.
REGISTER 14-1:
T3CON: TIMER3 CONTROL REGISTER
R/W-0
RD16
T3CCP2
T3CKPS1
T3CKPS0
T3CCP1
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
T3CCP2:T3CCP1: Timer3 and Timer1 to CCPx Enable bits
1x
= Timer3 is the clock source for compare/capture of CCP1 and CCP2 modules
01
= Timer3 is the clock source for compare/capture of CCP2 module,
Timer1 is the clock source for compare/capture of CCP1 module
00
= Timer1 is the clock source for compare/capture of CCP1 and CCP2 modules
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 Timer1 oscillator or 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