PIC16F688 Datasheet, PDF (65/174 Pages) Microchip Technology – 14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC16F688
8.0 ANALOG-TO-DIGITAL
CONVERTER (A/D) MODULE
The analog-to-digital converter (A/D) allows conversion
of an analog input signal to a 10-bit binary representa-
tion of that signal. The PIC16F688 has eight analog
inputs, multiplexed into one sample and hold circuit.
The output of the sample and hold is connected to the
input of the converter. The converter generates a
binary result via successive approximation and stores
the result in a 10-bit register. The voltage reference
used in the conversion is software selectable to either
VDD or a voltage applied by the VREF pin. Figure 8-1
shows the block diagram of the A/D on the PIC16F688.
FIGURE 8-1:
A/D BLOCK DIAGRAM
VDD
VREF
VCFG = 0
VCFG = 1
RA0/AN0
RA1/AN1/VREF
RA2/AN2
RA4/AN3
RC0/AN4
RC1/AN5
RC2/AN6
RC3/AN7
CHS<2:0>
A/D
GO/DONE
10
ADON
VSS
ADFM
10
ADRESH ADRESL
8.1 A/D Configuration and Operation
There are three registers available to control the
functionality of the A/D module:
1. ANSEL (Register 8-1)
2. ADCON0 (Register 8-2)
3. ADCON1 (Register 8-3)
8.1.1 ANALOG PORT PINS
The ANS<7:0> bits (ANSEL<7:0>) and the TRIS bits
control the operation of the A/D port pins. Set the
corresponding TRIS bits to set the pin output driver to
its high-impedance state. Likewise, set the
corresponding ANSEL bit to disable the digital input
buffer.
Note:
Analog voltages on any pin that is defined
as a digital input may cause the input
buffer to conduct excess current.
8.1.2 CHANNEL SELECTION
There are eight analog channels on the PIC16F688,
AN0 through AN7. The CHS<2:0> bits
(ADCON0<4:2>) control which channel is connected to
the sample and hold circuit.
8.1.3 VOLTAGE REFERENCE
There are two options for the voltage reference to the
A/D converter: either VDD is used, or an analog voltage
applied to VREF is used. The VCFG bit (ADCON0<6>)
controls the voltage reference selection. If VCFG is set,
then the voltage on the VREF pin is the reference;
otherwise, VDD is the reference.
 2004 Microchip Technology Inc.
Preliminary
DS41203B-page 63