Microchip Technology AC244045 Data Sheet
PIC16F72X/PIC16LF72X
DS41341E-page 100
© 2009 Microchip Technology Inc.
9.1
ADC Configuration
When configuring and using the ADC the following
functions must be considered:
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. Refer to Section 6.0
“I/O Ports” for more information.
digital signals. When converting analog signals, the I/O
pin should be configured for analog by setting the
associated TRIS and ANSEL bits. Refer to Section 6.0
“I/O Ports” 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.
channel is connected to the sample and hold circuit.
When changing channels, a delay is required before
starting the next conversion. Refer to Section 9.2
“ADC Operation” for more information.
starting the next conversion. Refer to Section 9.2
“ADC Operation” for more information.
9.1.3
ADC V
OLTAGE REFERENCE
The ADREF bits of the ADCON1 register provides
control of the positive voltage reference. The positive
voltage reference can be either V
control of the positive voltage reference. The positive
voltage reference can be either V
DD
, an external
voltage source or the internal Fixed Voltage Reference.
The negative voltage reference is always connected to
the ground reference. See Section 10.0 “Fixed
Voltage Reference” for more details on the Fixed
Voltage Reference.
The negative voltage reference is always connected to
the ground reference. See Section 10.0 “Fixed
Voltage Reference” for more details on the Fixed
Voltage Reference.
9.1.4
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:
able via the ADCS bits of the ADCON1 register. There
are seven possible clock options:
• F
OSC
/2
• F
OSC
/4
• F
OSC
/8
• F
OSC
/16
• F
OSC
/32
• F
OSC
/64
• F
RC
(dedicated internal oscillator)
The time to complete one bit conversion is defined as
T
T
AD
. One full 8-bit conversion requires 10 T
AD
periods
as shown in Figure 9-2.
For correct conversion, the appropriate T
AD
specifica-
tion must be met. Refer to the A/D conversion require-
ments in Section 23.0 “Electrical Specifications” for
more information. Table 9-1 gives examples of appro-
priate ADC clock selections.
ments in Section 23.0 “Electrical Specifications” for
more information. Table 9-1 gives examples of appro-
priate ADC clock selections.
Note:
Analog voltages on any pin that is defined
as a digital input may cause the input
buffer to conduct excess current.
as a digital input may cause the input
buffer to conduct excess current.
Note:
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.
ADC clock frequency, which may
adversely affect the ADC result.