PIC18F2480/2580/4480/4580
A simplified block diagram of the Timer3 module is
shown in Figure 15-1. A block diagram of the module’s
operation in Read/Write mode is shown in Figure 15-2.
15.0 TIMER3 MODULE
The Timer3 module timer/counter incorporates these
features:
The Timer3 module is controlled through the T3CON
register (Register 15-1). It also selects the clock source
options for the CCP modules (see Section 16.1.1
“CCP Modules and Timer Resources” for more
information).
• Software-selectable operation as a 16-bit timer or
counter
• Readable and writable 8-bit registers (TMR3H
and TMR3L)
• Selectable clock source (internal or external) with
device clock or Timer1 oscillator internal options
• Interrupt-on-overflow
• Module Reset on CCP Special Event Trigger
REGISTER 15-1: T3CON: TIMER3 CONTROL REGISTER
R/W-0
RD16
R/W-0
T3ECCP1(1)
R/W-0
R/W-0
R/W-0
T3CCP1(1)
R/W-0
R/W-0
R/W-0
T3CKPS1
T3CKPS0
T3SYNC
TMR3CS
TMR3ON
bit 7
bit 0
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
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
T3ECCP1:T3CCP1: Timer3 and Timer1 to CCP/ECCP Enable bits(1)
1x= Timer3 is the capture/compare clock source for both CCP and ECCP modules
01= Timer3 is the capture/compare clock source for ECCP;
Timer1 is the capture/compare clock source for CCP
00= Timer1 is the capture/compare clock source for both CCP and ECCP modules
bit 5-4
bit 2
T3CKPS<1:0>: 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 device 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
Note 1: These bits and the ECCP module are available on PIC18F4X80 devices only.
© 2009 Microchip Technology Inc.
DS39637D-page 163
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