Datasheet

© 2007 Microchip Technology Inc. DS39605F-page 111
PIC18F1220/1320
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
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.
REGISTER 14-1: T3CON: TIMER3 CONTROL REGISTER
R/W-0 U-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
RD16
— T3CKPS1 T3CKPS0 T3CCP1 T3SYNC TMR3CS TMR3ON
bit 7 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 Unimplemented: Read as ‘0’
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 3 T3CCP1: Timer3 and Timer1 to CCP1 Enable bits
1 = Timer3 is the clock source for compare/capture CCP module
0 = Timer1 is the clock source for compare/capture CCP module
bit 2 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 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
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