Datasheet

 1998-2013 Microchip Technology Inc. DS30289C-page 101
PIC17C7XX
13.0 TIMER1, TIMER2, TIMER3,
PWMS AND CAPTURES
The PIC17C7XX has a wealth of timers and time based
functions to ease the implementation of control applica-
tions. These time base functions include three PWM
outputs and four Capture inputs.
Timer1 and Timer2 are two 8-bit incrementing timers,
each with an 8-bit period register (PR1 and PR2, respec-
tively) and separate overflow interrupt flags. Timer1 and
Timer2 can operate either as timers (increment on inter-
nal F
OSC/4 clock), or as counters (increment on falling
edge of external clock on pin RB4/TCLK12). They are
also software configurable to operate as a single 16-bit
timer/counter. These timers are also used as the time
base for the PWM (Pulse Width Modulation) modules.
Timer3 is a 16-bit timer/counter which uses the TMR3H
and TMR3L registers. Timer3 also has two additional
registers (PR3H/CA1H:PR3L/CA1L) that are config-
urable as a 16-bit period register or a 16-bit capture
register. TMR3 can be software configured to incre-
ment from the internal system clock (F
OSC/4), or from
an external signal on the RB5/TCLK3 pin. Timer3 is the
time base for all of the 16-bit captures.
Six other registers comprise the Capture2, Capture3,
and Capture4 registers (CA2H:CA2L, CA3H:CA3L,
and CA4H:CA4L).
Figure 13-1, Figure 13-2 and Figure 13-3 are the con-
trol registers for the operation of Timer1, Timer2 and
Timer3, as well as PWM1, PWM2, PWM3, Capture1,
Capture2, Capture3 and Capture4.
Table 13-1 shows the Timer resource requirements for
these time base functions. Each timer is an open
resource so that multiple functions may operate with it.
TABLE 13-1: TIME-BASE FUNCTION/
RESOURCE REQUIREMENTS
REGISTER 13-1: TCON1 REGISTER (ADDRESS: 16h, BANK 3)
Time Base Function Timer Resource
PWM1 Timer1
PWM2 Timer1 or Timer2
PWM3 Timer1 or Timer2
Capture1 Timer3
Capture2 Timer3
Capture3 Timer3
Capture4 Timer3
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
CA2ED1 CA2ED0 CA1ED1 CA1ED0 T16 TMR3CS TMR2CS TMR1CS
bit 7 bit 0
bit 7-6 CA2ED1:CA2ED0: Capture2 Mode Select bits
00 = Capture on every falling edge
01 = Capture on every rising edge
10 = Capture on every 4th rising edge
11 = Capture on every 16th rising edge
bit 5-4 CA1ED1:CA1ED0: Capture1 Mode Select bits
00 = Capture on every falling edge
01 = Capture on every rising edge
10 = Capture on every 4th rising edge
11 = Capture on every 16th rising edge
bit 3 T16: Timer2:Timer1 Mode Select bit
1 = Timer2 and Timer1 form a 16-bit timer
0 = Timer2 and Timer1 are two 8-bit timers
bit 2 TMR3CS: Timer3 Clock Source Select bit
1 = TMR3 increments off the falling edge of the RB5/TCLK3 pin
0 = TMR3 increments off the internal clock
bit 1 TMR2CS: Timer2 Clock Source Select bit
1 = TMR2 increments off the falling edge of the RB4/TCLK12 pin
0 = TMR2 increments off the internal clock
bit 0 TMR1CS: Timer1 Clock Source Select bit
1 = TMR1 increments off the falling edge of the RB4/TCLK12 pin
0 = TMR1 increments off the internal clock
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
- n = Value at POR Reset ’1’ = Bit is set ’0’ = Bit is cleared x = Bit is unknown