Datasheet

ManualsBrandsMICROCHIP TECHNOLOGY ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller SOIC 14 8-Bit 20 MHz I/O number 11

PIC12F510/16F506

9.0 ANALOG-TO-DIGITAL (A/D)

CONVERTER

The A/D Converter allows conversion of an analog

signal into an 8-bit digital signal.

9.1 Clock Divisors

The ADC has 4 clock source settings ADCS<1:0>.

There are 3 divisor values 16, 8 and 4. The fourth set-

ting is INTOSC with a divisor of 4. These settings will

allow a proper conversion when using an external

oscillator at speeds from 20 MHz to 350 kHz. Using

an external oscillator at a frequency below 350 kHz

(TAD > 50 μs) requires the ADC oscillator setting to be

INTOSC/4 for valid ADC results.

The ADC requires 13 T

AD periods to complete a

conversion. The divisor values do not affect the number

of T

AD periods required to perform a conversion. The

divisor values determine the length of the T

AD period.

When the ADCS<1:0> bits are changed while an ADC

conversion is in process, the new ADC clock source will

not be selected until the next conversion is started. This

clock source selection will be lost when the device

enters Sleep.

9.1.1 VOLTAGE REFERENCE

There is no external voltage reference for the ADC. The

ADC reference voltage will always be V

DD.

9.1.2 ANALOG MODE SELECTION

The ANS<1:0> bits are used to configure pins for

analog input. Upon any Reset, ANS<1:0> defaults to

11. This configures pins AN0, AN1 and AN2 as analog

inputs. Pins configured as analog inputs are not avail-

able for digital output. Users should not change the

ANS bits while a conversion is in process. ANS bits are

active regardless of the condition of ADON.

9.1.3 ADC CHANNEL SELECTION

The CHS bits are used to select the analog channel to

be sampled by the ADC. The CHS<1:0> bits can be

changed at any time without adversely effecting a con-

version. To acquire an analog signal the CHS<1:0>

selection must match one of the pin(s) selected by the

ANS<1:0> bits. When the ADC is on (ADON = 1) and a

channel is selected that is also being used by the

comparator, then both the comparator and the ADC will

see the analog voltage on the pin.

When the CHS<1:0> bits are changed during an ADC

conversion, the new channel will not be selected until

the current conversion is completed. This allows the

current conversion to complete with valid results. All

channel selection information will be lost when the

device enters Sleep.

TABLE 9-1: CHANNEL SELECT (ADCS)

BITS AFTER AN EVENT

9.1.4 THE GO/DONE

BIT

The GO/DONE bit is used to determine the status of a

conversion, to start a conversion and to manually halt a

conversion in process. Setting the GO/DONE bit starts

a conversion. When the conversion is complete, the

ADC module clears the GO/DONE bit. A conversion

can be terminated by manually clearing the GO/DONE

bit while a conversion is in process. Manual termination

of a conversion may result in a partially converted

result in ADRES.

The GO/DONE

bit is cleared when the device enters

Sleep, stopping the current conversion. The ADC does

not have a dedicated oscillator, it runs off of the instruc-

tion clock. Therefore, no conversion can occur in sleep.

The GO/DONE

bit cannot be set when ADON is clear.

Note: It is the users responsibility to ensure that

use of the ADC and comparator simulta-

neously on the same pin, does not

adversely affect the signal being

monitored or adversely effect device

operation.

Event ADCS<1:0>

MCLR 11

Conversion completed CS<1:0>

Conversion terminated CS<1:0>

Power-on 11

Wake from Sleep 11