PIC18F2331 Datasheet, PDF (166/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
Note 1: Input capture prescalers are reset
(cleared) when the Input Capture module
is disabled (CAPxM = 0000).
2: When the Input Capture mode is changed
without first disabling the module and
entering the new Input Capture mode, a
false interrupt (or special event trigger on
IC1) may be generated. The user should
either (1) disable the Input Capture before
entering another mode or (2) disable IC
interrupts to avoid false interrupts during
IC mode changes.
3: During IC mode changes, the prescaler
count will not be cleared, therefore the
first capture in the new IC mode may be
from the non-zero prescaler.
16.1.1 EDGE CAPTURE MODE
In this mode, the value of the time base is captured
either on every rising edge, every falling edge, every
4th rising edge, or every 16th rising edge. The edge
present on the input capture pin (CAP1, CAP2 or
CAP3) is sampled by the synchronizing latch. The
signal is used to load the input capture buffer (ICxBUF
register) on the following Q1 clock (see Figure 16-4).
Consequently, Timer5 is either reset to ‘0’ (Q1
immediately following the capture event) or left free
running, depending on the setting of Capture Reset
Enable, CAPxREN, in the CAPxCON register.
Note:
On the first capture edge following the
setting of the Input Capture mode (i.e.,
MOVWF CAP1CON), Timer5 contents are
always captured into the corresponding
input capture buffer (i.e., CAPxBUF).
Timer5 can optionally be reset; however,
this is dependent on the setting of the
Capture Reset Enable bit (CAPxREN),
see Figure 16-4.
FIGURE 16-4:
EDGE CAPTURE MODE TIMING
Q1Q2 Q3 Q4 Q1Q2Q3Q4 Q1Q2Q3 Q4 Q1Q2Q3Q4 Q1Q2 Q3 Q4 Q1Q2Q3Q4Q1Q2Q3Q4 Q1Q2 Q3 Q4 Q1Q2Q3Q4 Q1Q2Q3Q4
OSC
TMR5⁽¹⁾
CAP1 pin⁽²⁾
0012
0013 0014
0015
0000 0001
0002
0000 0001
0002
CAP1BUF⁽³⁾
TMR5 reset⁽⁴⁾
Instruction _{MOVWF CAP1CON}
Execution
ABCD
0016
0003
BCF CAP1CON, CAP1REN
0002
Note 5
Note 1: TMR5 is a synchronous time base input to the Input Capture, prescaler = 1:1. It increments on Q1 rising edge.
2: IC1 is configured in Edge Capture mode (CAP1M3:CAP1M0 = 0010) with the time base reset upon edge capture
(CAP1REN = 1) and no noise filter.
3: TMR5 value is latched by CAP1BUF on TCY. In the event that a write to TMR5 coincides with an input capture event,
the write will always take precedence. All input capture buffers, CAP1BUF, CAP2BUF and CAP3BUF, are updated with
the incremented value of the time base on the next TCY clock edge when the capture event takes place (see Note 4
when Reset occurs).
4: TMR5 Reset is normally an asynchronous reset signal to TMR5. When used with the input capture, it is active immedi-
ately after the time base value is captured.
5: TMR5 Reset pulse is disabled by clearing CAP1REN bit (e.g, BCF CAP1CON, CAP1REN).
DS39616B-page 164
Preliminary
 2003 Microchip Technology Inc.