Microchip Technology MCP1631RD-MCC2 Data Sheet

DS41291G-page 104

 2006-2012 Microchip Technology Inc.

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
• Results formatting

9.1.1

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. See the corresponding Port
section for more information.

9.1.2

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 

 for more information.

9.1.3

ADC V

OLTAGE REFERENCE

The VCFG bits of the ADCON1 register provide
independent control of the positive and negative
voltage references. The positive voltage reference can
be either V

DD

 or an external voltage source. Likewise,

the negative voltage reference can be either V

SS

 or an

external voltage source.

9.1.4

 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:
• F

OSC

/2

• F

OSC

/8

• F

OSC

/32

• F

RC

 (dedicated internal oscillator)

The time to complete one bit conversion is defined as
T

AD

. One full 10-bit conversion requires 11 T

AD

 periods

as shown in 

.

For correct conversion, the appropriate T

AD

 specification

must be met. See A/D conversion requirements in

 for more

information. 

 gives examples of appropriate

ADC clock selections.

Analog voltages on any pin that is defined
as a digital input may cause the input buf-
fer to conduct excess current.

Unless using the F

RC

, any changes in the

system clock frequency will change the
ADC clock frequency, which may
adversely affect the ADC result.