Digilent 410-297P-KIT - Manual (Page 15)

ChipKIT MX3 Board Reference Manual
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• 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-.
The analog reference input pins are shared with two of the analog inputs. Vref- is shared with A3 (AN1/RB1), and
Vref+ is shared with A2 (AN0/RB0). These pins are not available to be used as analog inputs when being used as an
external reference.
When using the MPIDE software, the use of external analog references is selected using the analogReference()
function. The following values can be used with analogReference():
• DEFAULT – Vref- = 0V, Vref+ = 3.3V
• INTERNAL – same as default
• EXTERNAL – Vref- = 0V, Vref+ = voltage at A2
• EXTMINUS – Vref- = voltage at A3, Vref+ = 3.3V
• EXTPLUSMINUS – Vref- = voltage at A3, Vref+ = voltage at A2
11 Timers
The PIC32 microcontroller provides five timers that can be used for various timing functions. These timers are each
16 bits wide, although two pairs, TIMER2/TIMER3 and TIMER4/TIMER5, can be combined to produce 32 bit wide
timers.
A timer consists of a control register, a counter register, and a period register. The control register is used to
configure the timer for various modes of operation. The count register counts cycles of the clock source selected
via the control register. This clock source can be the peripheral bus clock or a division of the peripheral bus clock
via a prescaler divider. The period register can be used to generate an interrupt and/or reset the count register
when a predetermined value is reached.