PIC16F16-ESLASHP datasheet(40/136 Pages) MICROCHIP

40 / 136 page

PIC16F716

DS41206B-page 38

7.1

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

7.1.1

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 ADCON1 bits. See the corresponding Port

section for more information.

7.1.2

CHANNEL SELECTION

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 7.2

“ADC Operation” for more information.

7.1.3

ADC VOLTAGE REFERENCE

The PCFG bits of the ADCON0 register provide

independent control of the positive voltage reference.

The positive voltage reference can be either VDD or an

external voltage source.

7.1.4

CONVERSION CLOCK

The source of the conversion clock is software select-

able via the ADCS bits of the ADCON0 register. There

are four possible clock options:

•FOSC/2

•FOSC/8

•FOSC/32

•FRC (dedicated internal oscillator)

The time to complete one bit conversion is defined as

TAD. One full 8-bit conversion requires 9.5 TAD periods.

For correct conversion, the appropriate TAD specification

must be met. See A/D conversion requirements in

Section 12.0 “Electrical Characteristics” for more

information. Table 7-1 gives examples of appropriate

ADC clock selections.

TABLE 7-1:

TAD vs. DEVICE OPERATING FREQUENCIES

Note:

Analog voltages on any pin that is defined

as a digital input may cause the input

buffer 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.

AD Clock Source (TAD)

Device Frequency

Operation

ADCS<1:0>

20 MHz

5 MHz

1.25 MHz

333.33 kHz

2TOSC

100 ns(2)

400 ns(2)

1.6

μs6 μs

8TOSC

400 ns(2)

1.6

μs6.4 μs

μs(3)

32 TOSC

1.6

μs6.4 μs

25.6

μs(3)

2-6

μs(1), (4)

2-6

μs(1), (4)

2-6

μs(1), (4)

2-6

μs(1)

Legend: Shaded cells are outside of recommended range.

Note 1:

The RC source has a typical TAD time of 4

μs.

These values violate the minimum required TAD time.

For faster conversion times, the selection of another clock source is recommended.

When device frequency is greater than 1 MHz, the RC A/D conversion clock source is recommended for

Sleep operation only.

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