PIC16F631/677/685/687/689/690
7.0
TIMER2 MODULE
The Timer2 module is an eight-bit timer with the
following features:
•
•
•
•
•
8-bit timer register (TMR2)
8-bit period register (PR2)
Interrupt on TMR2 match with PR2
Software programmable prescaler (1:1, 1:4, 1:16)
Software programmable postscaler (1:1 to 1:16)
The TMR2 and PR2 registers are both fully readable
and writable. On any Reset, the TMR2 register is set to
00h and the PR2 register is set to FFh.
Timer2 is turned on by setting the TMR2ON bit in the
T2CON register to a ‘1’. Timer2 is turned off by clearing
the TMR2ON bit to a ‘0’.
The Timer2 prescaler is controlled by the T2CKPS bits
in the T2CON register. The Timer2 postscaler is
controlled by the TOUTPS bits in the T2CON register.
The prescaler and postscaler counters are cleared
when:
• A write to TMR2 occurs.
• A write to T2CON occurs.
• Any device Reset occurs (Power-on Reset, MCLR
Reset, Watchdog Timer Reset or Brown-out
Reset).
Note:
TMR2 is not cleared when T2CON is
written.
See Figure 7-1 for a block diagram of Timer2.
7.1
Timer2 Operation
The clock input to the Timer2 module is the system
instruction clock (F
OSC
/4). The clock is fed into the
Timer2 prescaler, which has prescale options of 1:1,
1:4 or 1:16. The output of the prescaler is then used to
increment the TMR2 register.
The values of TMR2 and PR2 are constantly compared
to determine when they match. TMR2 will increment
from 00h until it matches the value in PR2. When a
match occurs, two things happen:
• TMR2 is reset to 00h on the next increment cycle.
• The Timer2 postscaler is incremented
The match output of the Timer2/PR2 comparator is fed
into the Timer2 postscaler. The postscaler has
postscale options of 1:1 to 1:16 inclusive. The output of
the Timer2 postscaler is used to set the TMR2IF
interrupt flag bit in the PIR1 register.
FIGURE 7-1:
TIMER2 BLOCK DIAGRAM
TMR2
Output
Sets Flag
bit TMR2IF
F
OSC
/4
Prescaler
1:1, 1:4, 1:16
2
T2CKPS<1:0>
TMR2
Reset
Comparator
EQ
PR2
Postscaler
1:1 to 1:16
4
TOUTPS<3:0>
©
2007 Microchip Technology Inc.
DS41262D-page 91
MICROCHIP [ MICROCHIP TECHNOLOGY ]
