PIC18LF4331 datasheet(157/392 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS39616D-page 157

PIC18F2331/2431/4331/4431

17.1.2

PERIOD MEASUREMENT MODE

The Period Measurement mode is selected by setting

CAPxM<3:0> = 0101. In this mode, the value of Timer5

is latched into the CAPxBUF register on the rising edge

of the input capture trigger and Timer5 is subsequently

reset to 0000h (optional by setting CAPxREN = 1) on

the next TCY (see capture and Reset relationship in

Figure 17-4).

17.1.3

PULSE-WIDTH MEASUREMENT

MODE

The Pulse-Width Measurement mode can be configured

for two different edge sequences, such that the pulse

width is based on either the falling to rising edge of the

CAPx input pin (CAPxM<3:0> = 0110), or on the rising

to falling edge (CAPxM<3:0> = 0111).

Timer5 is always reset on the edge when the

measurement is first initiated. For example, when the

measurement is based on the falling to rising edge,

Timer5 is first reset on the falling edge, and thereafter,

the timer value is captured on the rising edge. Upon

entry into the Pulse-Width Measurement mode, the

very first edge detected on the CAPx pin is always

captured. The TMR5 value is reset on the first active

edge (see Figure 17-5).

FIGURE 17-5:

PULSE-WIDTH MEASUREMENT MODE TIMING

CAP1 Pin(2)

0000

0002

0000

0001

0002

TMR5(1)

CAP1BUF(3)

0002

0014

0013

0012

0015

0001

TMR5 Reset(4,5)

MOVWF CAP1CON

Instruction

0001

Note 1:

TMR5 is a synchronous time base input to the input capture; prescaler = 1:1. It increments on every Q1 rising edge.

IC1 is configured in Pulse-Width Measurement mode (CAP1M<3:0> = 0111, rising to falling pulse-width

measurement). No noise filter on CAP1 input is used. The MOVWF instruction loads CAP1CON when W = 0111.

TMR5 value is latched by CAP1BUF on TCY rising edge. In the event that a write to TMR5 coincides with an input cap-

ture 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).

TMR5 Reset is normally an asynchronous Reset signal to TMR5. When used in Pulse-Width Measurement mode, it

is always present on the edge that first initiates the pulse-width measurement (i.e., when configured in the rising to

falling Pulse-Width Measurement mode); it is active on each rising edge detected. In the falling to rising Pulse-Width

Measurement mode, it is active on each falling edge detected.

TMR5 Reset pulse is activated on the capture edge. The CAP1REN bit has no bearing in this mode.

Execution(2)

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1Q2 Q3 Q4 Q1Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

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