PIC16F87X
7.1
Timer2 Prescaler and Postscaler
7.0
TIMER2 MODULE
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 CCP module(s). The TMR2 reg-
ister is readable and writable, and is cleared on any
device reset.
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 (POR, MCLR reset, WDT reset
or BOR)
The input clock (FOSC/4) has a prescale option of 1:1,
1:4
or
1:16,
selected
by
control
bits
TMR2 is not cleared when T2CON is written.
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 ini-
tialized to FFh upon reset.
7.2
Output of TMR2
The output of TMR2 (before the postscaler) is fed to the
SSPort module, which optionally uses it to generate
shift clock.
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>)).
FIGURE 7-1: TIMER2 BLOCK DIAGRAM
Sets flag
TMR2
output (1)
bit TMR2IF
Timer2 can be shut off by clearing control bit TMR2ON
(T2CON<2>) to minimize power consumption.
Reset
Prescaler
1:1, 1:4, 1:16
TMR2 reg
FOSC/4
Register 7-1 shows the Timer2 control register.
Postscaler
2
Comparator
Additional information on timer modules is available in
the PICmicro™ Mid-Range MCU Family Reference
Manual (DS33023).
1:1 to 1:16
EQ
T2CKPS1:
T2CKPS0
4
PR2 reg
T2OUTPS3:
T2OUTPS0
Note 1: TMR2 register output can be software selected
by the SSP module as a baud clock.
REGISTER 7-1: T2CON: TIMER2 CONTROL REGISTER (ADDRESS 12h)
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
bit0
R
W
U
= Readable bit
= Writable bit
= Unimplemented bit,
read as ‘0’
bit7
- n = Value at POR reset
bit 7:
Unimplemented: Read as '0'
bit 6-3: TOUTPS3:TOUTPS0: Timer2 Output Postscale Select bits
0000= 1:1 Postscale
0001= 1:2 Postscale
0010= 1:3 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
1999 Microchip Technology Inc.
DS30292B-page 55
ETC [ ETC ]
