PIC18FXX20
Figure 14-1 is a simplified block diagram of the Timer3
module.
Register 14-1 shows the Timer3 control register. This
register controls the Operating mode of the Timer3
module and sets the CCP clock source.
Register 12-1 shows the Timer1 control register. This
register controls the Operating mode of the Timer1
module, as well as contains the Timer1 oscillator
enable bit (T1OSCEN), which can be a clock source for
Timer3.
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
REGISTER 14-1: T3CON: TIMER3 CONTROL REGISTER
R/W-0
RD16
bit 7
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
T3CCP2 T3CKPS1 T3CKPS0 T3CCP1 T3SYNC TMR3CS TMR3ON
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
11=Timer3 and Timer4 are the clock sources for CCP1 through CCP5
10=Timer3 and Timer4 are the clock sources for CCP3 through CCP5;
Timer1 and Timer2 are the clock sources for CCP1 and CCP2
01=Timer3 and Timer4 are the clock sources for CCP2 through CCP5;
Timer1 and Timer2 are the clock sources for CCP1
00=Timer1 and Timer2 are the clock sources for CCP1 through CCP5
bit 5-4
bit 2
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
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
bit 0
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)
TMR3ON: Timer3 On bit
1= Enables Timer3
0= Stops Timer3
Legend:
R = Readable bit
- n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
2003 Microchip Technology Inc.
Advance Information
DS39609A-page 143
MICROCHIP [ MICROCHIP ]
