41594B datasheet(126/372 Pages) MICROCHIP

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PIC12LF1840T48A

DS41594B-page 126

Preliminary

 2011-2012 Microchip Technology Inc.

16.1

ADC Configuration

When configuring and using the ADC the following

functions must be considered:

• Port configuration

• Channel selection

• ADC voltage reference selection

• ADC conversion clock source

• Interrupt control

• Result formatting

16.1.1

PORT CONFIGURATION

The ADC can be used to convert both analog and

digital signals. When converting analog signals, the I/O

pin should be configured for analog by setting the

associated

TRIS

and

ANSEL

bits.

Refer

Section 12.0 “I/O Ports” for more information.

16.1.2

CHANNEL SELECTION

There are seven channel selections available:

• AN<3:0> pins

• Temperature Indicator

• DAC Output

• FVR (Fixed Voltage Reference) Output

Refer to Section 17.0 “Digital-to-Analog Converter

(DAC) Module”, Section 14.0 “Fixed Voltage Refer-

ence (FVR)” and Section 15.0 “Temperature Indica-

tor Module” for more information on these channel

selections.

The CHS bits of the ADCON0 register determine which

channel is connected to the sample and hold circuit.

When changing channels, a delay is required before

starting the next conversion. Refer to Section 16.2

“ADC Operation” for more information.

16.1.3

ADC VOLTAGE REFERENCE

The ADPREF bits of the ADCON1 register provides

control of the positive voltage reference. The positive

voltage reference can be:

•VREF+ pin

•VDD

• FVR 2.048V

See Section 14.0 “Fixed Voltage Reference (FVR)”

for more details on the Fixed Voltage Reference.

16.1.4

CONVERSION CLOCK

The source of the conversion clock is software select-

able via the ADCS bits of the ADCON1 register. There

are seven possible clock options:

•FOSC/2

•FOSC/4

•FOSC/8

•FOSC/16

•FOSC/32

•FOSC/64

•FRC (dedicated internal oscillator)

The time to complete one bit conversion is defined as

TAD. One full 10-bit conversion requires 11.5 TAD

periods as shown in Figure 16-2.

For correct conversion, the appropriate TAD specifica-

tion must be met. Refer to the A/D conversion require-

ments in Section 31.0 “Electrical Specifications” for

more information. Table 16-1 gives examples of

appropriate ADC clock selections.

Note:

Analog voltages on any pin that is defined

as a digital input may cause the input buf-

fer to conduct excess current.

Note:

Unless using the FRC, any changes in the

system clock frequency will change the

ADC

clock

frequency,

which

may

adversely affect the ADC result.

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