Datasheet

© 2009 Microchip Technology Inc. DS39761C-page 161
PIC18F2682/2685/4682/4685
14.0 TIMER3 MODULE
The Timer3 timer/counter module incorporates these
features:
• 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 CCP1 Special Event Trigger
A simplified block diagram of the Timer3 module is
shown in Figure 14-1. A block diagram of the module’s
operation in Read/Write mode is shown in Figure 14-2.
The Timer3 module is controlled through the T3CON
register (Register 14-1). It also selects the clock source
options for the ECCP1/CCP1 modules (see
Section 15.1.1 “CCP1 Modules and Timer
Resources” for more information).
REGISTER 14-1: T3CON: TIMER3 CONTROL REGISTER
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
RD16 T3ECCP1
(1)
T3CKPS1 T3CKPS0 T3CCP1
(1)
T3SYNC TMR3CS TMR3ON
bit 7 bit 0
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
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 ECCP1/CCP1 Enable bits
(1)
1x = Timer3 is the capture/compare clock source for both CCP1 and ECCP1 modules
01 = Timer3 is the capture/compare clock source for ECCP1;
Timer1 is the capture/compare clock source for CCP1
00 = Timer1 is the capture/compare clock source for both CCP1 and ECCP1 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 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 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 (F
OSC/4)
bit 0 TMR3ON: Timer3 On bit
1 = Enables Timer3
0 = Stops Timer3
Note 1: Thess bits and the ECCP1 module are available on PIC18F4682/4685 devices only.