mikroElektronika EasyPIC v7, Руководство пользователя

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Easy PIC
for dsPIC30
®
v7
page 30
Digital signals have two discrete states, which
are decoded as high and low, and interpreted
as logic 1 and logic 0. Analog signals, on the
other hand, are continuous, and can have any
value within defined range. A/D converters are
specialized circuits which can convert analog signals
(voltages) into a digital representation, usually in
form of an integer number. The value of this number
is linearly dependent on the input voltage value. Most
microcontrollers nowadays internally have A/D converters
connected to one or more input pins. Some of the most
important parameters of A/D converters are conversion time
and resolution. Conversion time determines how fast can an
analog voltage be represented in form of a digital number. This is an
important parameter if you need fast data acquisition. The other parameter
is resolution. Resolution represents the number of discrete steps that supported
voltage range can be divided into. It determines the sensitivity of the A/D converter.
Resolution is represented in maximum number of bits that resulting number occupies. Most PIC
®
microcontrollers have 12-bit resolution, meaning that maximum value of conversion can be represented with 12
bits, which converted to integer is 2
12
=4096. This means that supported voltage range, for example from 0-5V,
can be divided into 4096 discrete steps of about 1.22mV. We gave you the possibility to set microcontroller
voltage reference to 4.096V DC by putting jumper J10 (RBO/VREF+) to 4.096V position, Figure 17-2. This
can be done only when the power supply is 5V (jumper J16 in 5V position). In that case discrete steps are
1mV. When using voltage reference module, make sure to disconnect other peripherals from RB0 pin. EasyPIC
™
v7 for dsPIC30
®
provides an interface in form of potentiometer for simulating analog input voltages that can be
routed to any of the 7 supported analog input pins.
ADC inputs
P3
10K
R12
220
VCC-BRD
C6
100nF
J7
RB0
RB1
RB2
RB3
RB10
RB11
RB12
DATA BUS
Enabling ADC inputs
In order to connect the output of the
potentiometer P3 to RB0, RB1, RB2, RB3,
RB10, RB11 or RB12 analog microcontroller
inputs, you have to place the jumper J7 in the
desired position. By moving the potentiometer
knob, you can create voltages in range from
GND to VCC-BRD.
Figure 17-1:
Potentiometer output
connected to RB1
microcontroller pin
other modules
Figure 17-2: use jumper J10 to set microcontroller
voltage reference to 4.096V or VCC position
In order to set microcontroller voltage reference, you
must place jumper J10 (RBO/VREF+) to appropriate
position. Use 4.096 position ONLY when the jumper
J16 is in 5V position.