Digilent MX4cK Manuel d'utilisateur télécharger pdf (Page 19)

Cerebot MX4cK Reference Manual

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• A12 – JB-07, digital pin 12, RB15

• A13 – JB-10, digital pin 15, RB14

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 appear on

Pmod connector JK, pins 7 & 8. Vref- is on pin

JK-07, and Vref+ is on pin JK-08. These pins

are not available to be used for digital I/O when

being used as an external reference.

When using the chipKIT 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

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 pre-scaler divider.

The period register can be used to generate an

interrupt and/or reset the count register when a

pre-determined value is reached.

Each timer has an associated input pin. In

some operating modes, this pin can be used

as an external clock input to the timer, or as a

gate input to turn on/off incrementing of the

counter register under control of an external

signal.

The following gives the Pmod connector

position, chipKIT pin number, and

microcontroller I/O port and bit number for the

timer input pins.

• TCK1 – not available

• TCK2 – JD-04, digital pin 27, RC01

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 34 35

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