PIC18F23K22-ESLASHML datasheet(319/496 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

Preliminary

DS41412C-page 319

PIC18(L)F2X/4XK22

The module uses the edge Status bits to control the

current source output to external analog modules (such

as the A/D Converter). Current is only supplied to

external modules when only one (but not both) of the

Status bits is set, and shuts current off when both bits

are either set or cleared. This allows the CTMU to

measure current only during the interval between

edges. After both Status bits are set, it is necessary to

clear them before another measurement is taken. Both

bits should be cleared simultaneously, if possible, to

avoid re-enabling the CTMU current source.

In addition to being set by the CTMU hardware, the

edge Status bits can also be set by software. This is

also the user’s application to manually enable or

disable the current source. Setting either one (but not

both) of the bits enables the current source. Setting or

clearing both bits at once disables the source.

19.1.5

INTERRUPTS

The CTMU sets its interrupt flag (PIR3<2>) whenever

the current source is enabled, then disabled. An

interrupt is generated only if the corresponding

interrupt enable bit (PIE3<2>) is also set. If edge

sequencing is not enabled (i.e., Edge 1 must occur

before Edge 2), it is necessary to monitor the edge

Status bits and determine which edge occurred last and

caused the interrupt.

19.2

CTMU Module Initialization

The following sequence is a general guideline used to

initialize the CTMU module:

Select the current source range using the IRNG

bits (CTMUICON<1:0>).

Adjust the current source trim using the ITRIM

bits (CTMUICON<7:2>).

Configure the edge input sources for Edge 1 and

Edge 2 by setting the EDG1SEL and EDG2SEL

bits (CTMUCONL<3:2 and 6:5>).

Configure the input polarities for the edge inputs

using the EDG1POL and EDG2POL bits

(CTMUCONL<4,7>). The default configuration

is for negative edge polarity (high-to-low

transitions).

Enable edge sequencing using the EDGSEQEN

bit

(CTMUCONH<2>).

default,

edge

sequencing is disabled.

Select the operating mode (Measurement or

Time Delay) with the TGEN bit. The default

mode is Time/Capacitance Measurement.

Discharge the connected circuit by setting the

IDISSEN bit (CTMUCONH<1>); after waiting a

sufficient time for the circuit to discharge, clear

IDISSEN.

Disable the module by clearing the CTMUEN bit

(CTMUCONH<7>).

Enable the module by setting the CTMUEN bit.

10. Clear the Edge Status bits: EDG2STAT and

EDG1STAT (CTMUCONL<1:0>).

11. Enable both edge inputs by setting the EDGEN

bit (CTMUCONH<3>).

Depending on the type of measurement or pulse

generation being performed, one or more additional

modules may also need to be initialized and configured

with the CTMU module:

• Edge Source Generation: In addition to the

external edge input pins, both Timer1 and the

Output Compare/PWM1 module can be used as

edge sources for the CTMU.

• Capacitance or Time Measurement: The CTMU

module uses the A/D Converter to measure the

voltage across a capacitor that is connected to one

of the analog input channels.

• Pulse Generation: When generating system clock

independent output pulses, the CTMU module

uses Comparator 2 and the associated

comparator voltage reference.

PIC18F23K22-E/ML Datasheet(PDF) 319 Page - Microchip Technology

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