PIC18F2331 Datasheet, PDF (169/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
16.1.5 ENTERING INPUT CAPTURE MODE
AND CAPTURE TIMING
The following is a summary of functional operation
upon entering any of the Input Capture modes:
1. After the module is configured for one of the
capture modes by setting the Mode Select bits
(CAPxM3:CAPxM0), the first detected edge
captures Timer5 value and stores it in the CAPx-
BUF register. The timer is then reset (depending
on the setting of CAPxREN bit) and starts to
increment according to its settings, see
Figure 16-4, Figure 16-5 and Figure 16-6.
2. On all edges, the capture logic performs the fol-
lowing:
a) Input Capture mode is decoded and the
active edge is identified
b) The CAPxREN bit is checked to determine
whether Timer5 is reset or not.
c) On every active edge, the Timer5 value is
recorded in the input capture buffer (CAPx-
BUF).
d) Reset Timer5 after capturing the value of
the timer when CAPxREN bit is enabled.
Timer5 is reset on every active capture
edge in this case.
e) On all continuing capture edge events
repeat steps 1 through 4 until the Opera-
tional mode is terminated either by user
firmware, POR or BOR.
f) The timer value is not affected when switch-
ing into and out of various input capture
modes.
16.1.6 TIMER5 RESET
Every Input Capture trigger can optionally reset
(TMR5). Capture Reset Enable bit, CAPxREN, gates
the automatic Reset of the time base of the capture
event with this enable Reset signal. All capture events
reset the selected timer when CAPxREN is set. Resets
are disabled when CAPxREN is cleared (see
Figure 16-4, Figure 16-5 and Figure 16-6).
Note: The CAPxREN bit has no effect in Pulse
Width Measurement mode.
16.1.7 IC INTERRUPTS
There are four operating modes for which the IC
module can generate an interrupt and set one of the
Interrupt Capture flag bits (IC1IF, IC2QEIF or
IC3DRIF). The interrupt flag that is set depends on the
channel in which the event occurs. The modes are:
• Edge capture (CAPxM3:CAPxM0 = 0001, 0010,
0011 or 0100)
• Period measurement event
(CAPxM3:CAPxM0 = 0101)
• Pulse width measurement event
(CAPxM3:CAPxM0 = 0110 or 0111)
• State change event (CAPxM3:CAPxM0 = 1000)
Note:
The special event trigger is generated only
in the Special Event Trigger mode on
CAP1 input (CAP1M2:CAP1M0> = 1110
and 1111). IC1IF interrupt is not set in this
mode.
The timing of interrupt and special trigger events is
shown in Figure 16-7. Any active edge is detected on
the rising edge of Q2 and propagated on the rising
edge of Q4 rising edge. If an active edge happens to
occur any later than this (on the falling edge of Q2, for
example), then it will be recognized on the next Q2
rising edge.
 2003 Microchip Technology Inc.
Preliminary
DS39616B-page 167