PIC18F2220/2320/4220/4320
Figure 14-1 is a simplified block diagram of the Timer3
module.
14.0 TIMER3 MODULE
The Timer3 module timer/counter has the following
features:
Register 14-1 shows the Timer3 Control register. This
register controls the operating mode of the Timer3
module and sets the CCP clock source.
• 16-bit timer/counter (two 8-bit registers: TMR3H
and TMR3L)
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.
• Readable and writable (both registers)
• Internal or external clock select
• Interrupt-on-overflow from FFFFh to 0000h
• Reset from CCP module trigger
REGISTER 14-1: T3CON: TIMER3 CONTROL REGISTER
R/W-0
RD16
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
T3CCP2 T3CKPS1 T3CKPS0 T3CCP1 T3SYNC TMR3CS TMR3ON
bit 0
bit 7
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 T3CCP2:T3CCP1: Timer3 and Timer1 to CCPx Enable bits
1x= Timer3 is the clock source for compare/capture CCP modules
01= Timer3 is the clock source for compare/capture of CCP2,
Timer1 is the clock source for compare/capture of CCP1
00= Timer1 is the clock source for compare/capture CCP 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 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
bit 0
TMR3CS: Timer3 Clock Source Select bit
1= External clock input from Timer1 oscillator or T1CKI (on the rising edge after the first
falling edge)
0= Internal clock (FOSC/4)
TMR3ON: Timer3 On bit
1= Enables Timer3
0= Stops Timer3
Legend:
R = Readable bit
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
- n = Value at POR
2003 Microchip Technology Inc.
DS39599C-page 129
MICROCHIP [ MICROCHIP ]
