PIC18F2420/2520/4420/4520
14.0
TIMER3 MODULE
The Timer3 module timer/counter 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 CCP 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 CCP modules (see
for more
information).
REGISTER 14-1:
R/W-0
RD16
bit 7
Legend:
R = Readable bit
-n = Value at POR
bit 7
T3CON: TIMER3 CONTROL REGISTER
R/W-0
T3CKPS1
R/W-0
T3CKPS0
R/W-0
T3CCP1
R/W-0
T3SYNC
R/W-0
TMR3CS
R/W-0
TMR3ON
bit 0
R/W-0
T3CCP2
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
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
T3CCP<2:1>:
Timer3 and Timer1 to CCPx Enable bits
1x
= Timer3 is the capture/compare clock source for the CCP modules
01
= Timer3 is the capture/compare clock source for CCP2;
Timer1 is the capture/compare clock source for CCP1
00
= Timer1 is the capture/compare clock source for the CCP modules
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.
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)
TMR3ON:
Timer3 On bit
1
= Enables Timer3
0
= Stops Timer3
bit 6,3
bit 5-4
bit 2
bit 1
bit 0
©
2008 Microchip Technology Inc.
DS39631E-page 135
MICROCHIP [ MICROCHIP TECHNOLOGY ]
