PIC18F2220/2320/4220/4320
13.1 Timer2 Operation
13.0 TIMER2 MODULE
Timer2 can be used as the PWM time base for the
PWM mode of the CCP module. The TMR2 register is
readable and writable and is cleared on any device
Reset. The input clock (FOSC/4) has a prescale option
of 1:1, 1:4 or 1:16, selected by control bits,
T2CKPS1:T2CKPS0 (T2CON<1:0>). The match out-
put of TMR2 goes through a 4-bit postscaler (which
gives a 1:1 to 1:16 scaling inclusive) to generate a
TMR2 interrupt (latched in flag bit, TMR2IF (PIR1<1>)).
The Timer2 module timer has the following features:
• 8-bit timer (TMR2 register)
• 8-bit period register (PR2)
• Readable and writable (both registers)
• Software programmable prescaler (1:1, 1:4, 1:16)
• Software programmable postscaler (1:1 to 1:16)
• Interrupt on TMR2 match with PR2
• SSP module optional use of TMR2 output to
generate clock shift
The prescaler and postscaler counters are cleared
when any of the following occurs:
Timer2 has a control register shown in Register 13-1.
TMR2 can be shut-off by clearing control bit, TMR2ON
(T2CON<2>), to minimize power consumption.
Figure 13-1 is a simplified block diagram of the Timer2
module. Register 13-1 shows the Timer2 Control regis-
ter. The prescaler and postscaler selection of Timer2
are controlled by this register.
• A write to the TMR2 register
• A write to the T2CON register
• Any device Reset (Power-on Reset, MCLR Reset,
Watchdog Timer Reset or Brown-out Reset)
TMR2 is not cleared when T2CON is written.
REGISTER 13-1: T2CON: TIMER2 CONTROL REGISTER
U-0
—
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
TOUTPS3 TOUTPS2 TOUTPS1 TOUTPS0 TMR2ON T2CKPS1 T2CKPS0
bit 0
bit 7
bit 7
Unimplemented: Read as ‘0’
bit 6-3 TOUTPS3:TOUTPS0: Timer2 Output Postscale Select bits
0000= 1:1 postscale
0001= 1:2 postscale
•
•
•
1111= 1:16 postscale
bit 2
TMR2ON: Timer2 On bit
1= Timer2 is on
0= Timer2 is off
bit 1-0 T2CKPS1:T2CKPS0: Timer2 Clock Prescale Select bits
00= Prescaler is 1
01= Prescaler is 4
1x= Prescaler is 16
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 127
MICROCHIP [ MICROCHIP ]
