PIC18F2220/2320/4220/4320
13.0
•
•
•
•
•
•
•
TIMER2 MODULE
13.1
Timer2 Operation
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
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 (F
OSC
/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 prescaler and postscaler counters are cleared
when any of the following occurs:
• 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.
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.
module. Register 13-1 shows the Timer2 Control regis-
ter. The prescaler and postscaler selection of Timer2
are controlled by this register.
REGISTER 13-1:
T2CON: TIMER2 CONTROL REGISTER
U-0
—
bit 7
R/W-0
TOUTPS3
R/W-0
TOUTPS2
R/W-0
TOUTPS1
R/W-0
TOUTPS0
R/W-0
R/W-0
R/W-0
T2CKPS0
bit 0
TMR2ON T2CKPS1
bit 7
bit 6-3
Unimplemented:
Read as ‘0’
TOUTPS3:TOUTPS0:
Timer2 Output Postscale Select bits
0000
= 1:1 postscale
0001
= 1:2 postscale
•
•
•
1111
= 1:16 postscale
TMR2ON:
Timer2 On bit
1
= Timer2 is on
0
= Timer2 is off
T2CKPS1:T2CKPS0:
Timer2 Clock Prescale Select bits
00
= Prescaler is 1
01
= Prescaler is 4
1x
= Prescaler is 16
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 2
bit 1-0
2003 Microchip Technology Inc.
DS39599C-page 127
MICROCHIP [ MICROCHIP TECHNOLOGY ]
