PIC18F44J50-I Datasheet, PDF (213/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

PIC18F46J50 FAMILY
15.0 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 ECCP Special Event Trigger
A simplified block diagram of the Timer3 module is
shown in Figure 15-1.
The Timer3 module is controlled through the T3CON
register (Register 15-1). It also selects the clock source
options for the ECCP modules; see Section 18.1.1
“ECCP Module and Timer Resources” for more
information.
The FOSC clock source (TMR3CS<1:0> = 01) should not
be used with the ECCP capture/compare features. If the
timer will be used with the capture or compare features,
always select one of the other timer clocking options.
REGISTER 15-1: T3CON: TIMER3 CONTROL REGISTER (ACCESS F79h)
R/W-0
TMR3CS1
bit 7
R/W-0
TMR3CS0
R/W-0
T3CKPS1
R/W-0
T3CKPS0
R/W-0
T3OSCEN
R/W-0
T3SYNC
R/W-0
RD16
R/W-0
TMR3ON
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 7-6
bit 5-4
bit 3
bit 2
bit 1
bit 0
TMR3CS<1:0>: Timer3 Clock Source Select bits
10 = Timer3 clock source is the Timer1 oscillator or the T3CKI digital input pin (assigned in PPS module)
01 = Timer3 clock source is the system clock (FOSC)⁽¹⁾
00 = Timer3 clock source is the instruction clock (FOSC/4)
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
T3OSCEN: Timer3 Oscillator Source Select bit
When TMR3CS<1:0> = 10:
1 = Power up the Timer1 crystal driver (T1OSC) and supply the Timer3 clock from the crystal output
0 = Timer1 crystal driver is off, Timer3 clock is from the T3CKI digital input pin assigned in PPS module⁽²⁾
When TMR3CS<1:0> = 0x:
1 = Power up the Timer1 crystal driver (T1OSC)
0 = Timer1 crystal driver is off⁽²⁾
T3SYNC: Timer3 External Clock Input Synchronization Control bit
When TMR3CS<1:0> = 10:
1 = Do not synchronize external clock input
0 = Synchronize external clock input
When TMR3CS<1:0> = 0x:
This bit is ignored; Timer3 uses the internal clock.
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
TMR3ON: Timer3 On bit
1 = Enables Timer3
0 = Stops Timer3
Note 1:
2:
The FOSC clock source should not be selected if the timer will be used with the ECCP capture/compare features.
The Timer1 oscillator crystal driver is powered whenever T1OSCEN (T1CON) or T3OSCEN (T3CON) = 1.
The circuit is enabled by the logical OR of these two bits. When disabled, the inverter and feedback resistor
are disabled to eliminate power drain. The TMR1ON and TMR3ON bits do not have to be enabled to power
up the crystal driver.
 2011 Microchip Technology Inc.
DS39931D-page 213