PIC16F818/819
8.0
TIMER2 MODULE
8.1
Timer2 Prescaler and Postscaler
Timer2 is an 8-bit timer with a prescaler and a
postscaler. It can be used as the PWM time base for the
PWM mode of the CCP1 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 Timer2 module has an 8-bit period register, PR2.
Timer2 increments from 00h until it matches PR2 and
then resets to 00h on the next increment cycle. PR2 is
a readable and writable register. The PR2 register is
initialized to FFh upon Reset.
The match output 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>)).
Timer2 can be shut-off by clearing control bit, TMR2ON
(T2CON<2>), to minimize power consumption.
Additional information on timer modules is available in
the
“PICmicro
®
Mid-Range MCU Family Reference
Manual”
(DS33023).
Postscaler
1:1 to 1:16
4
EQ
Comparator
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, WDT
Reset or Brown-out Reset)
TMR2 is not cleared when T2CON is written.
8.2
Output of TMR2
The output of TMR2 (before the postscaler) is fed to the
Synchronous Serial Port module which optionally uses
it to generate a shift clock.
FIGURE 8-1:
Sets Flag
bit TMR2IF
TMR2
Output
(1)
Reset
TIMER2 BLOCK DIAGRAM
TMR2 reg
Prescaler
1:1, 1:4, 1:16
2
F
OSC
/4
PR2 reg
Note 1:
TMR2 register output can be software
selected by the SSP module as a baud clock.
2004 Microchip Technology Inc.
DS39598E-page 63
MICROCHIP [ MICROCHIP TECHNOLOGY ]
