chipKIT™ MX3 Board Reference Manual
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9
Analog Inputs
The PIC32MX320 microcontroller provides a 10-bit analog to digital (A/D) converter that provides up to sixteen
analog inputs. The chipKIT MX3 board provides access to 11 inputs on the Pmod connectors. The converted values
produced by the A/D converter will be in the range 0–1023.
For detailed information on the operation and use of the A/D converter, refer to the PIC32 Family Reference
Manual, Section 17, 10-bit AD Converter.
The analog inputs are accessed using the analogRead() function in the MPIDE software. The analog input pin
number is specified using the symbols A0–A10. The digital pin numbers for the pin or the numbers 0–10 can also
be used, but using the symbols A0–A10 is recommended.
The following gives the Pmod connector position, digital pin number, and microcontroller I/O port and bit number
for the analog inputs:
A0 – JC-01, digital pin 16, RB8
A1 – JC-04, digital pin 19, RB14
A2 – JC-07, digital pin 20, RB0
A3 – JC-08, digital pin 21, RB1
A4 – JD-01, digital pin 24, RB2
A5 – JD-04, digital pin 27, RB9
A6 – JD-07, digital pin 28, RB12
A7 – JD-10, digital pin 31, RB13
A8 – JE-08, digital pin 37, RB5
A9 – JE-09, digital pin 38, RB4
A10 – JE-10, digital pin 39, RB3
10 A/D Converter Reference
The PIC32 microcontroller provides two reference inputs to the analog to digital converter. Vref- is used set the
lower reference level and Vref+ is used to set the upper reference level. These references can be connected to
internal references or external references using two of the analog input pins.
When the internal references are being used, Vref- is connected to Vss and Vref+ is connected to Vdd. This means
that the voltage input range at the analog input pins is 0V–3.3V. In this case, an input voltage of 0V will convert to
~0, an input voltage of 1.65V will convert to ~511, and an input voltage of 3.3V will convert to ~1023.
Either one, or both, of the references can be connected to external reference pins. When this is done, the
references can be set to voltages other than 0V and 3.3V.
If, for example, both references were selected to use external references, with 1V applied to Vref- and 2V applied
to Vref+, the input voltage range at the analog input pins would be from 1V to 2V. An applied voltage of 1V would
have a converted value of ~0, 1.5V would have a converted value of ~511, and 2V would have a converted value of
~1023.
When both external references are being used, Vref+ must have a higher voltage applied to in than Vref-.