Datasheet
MPLAB
®
Starter Kit for Intelligent.Integrated.Analog User’s Guide
DS50002172A-page 20 2013 Microchip Technology Inc.
2.2.1 Clock Demo
The 24-hour clock is the home page for the demo. This is a 24-hour clock with a blinking
colon for seconds. The clock uses the on-board 32 kHz Secondary Oscillator (SOSC)
for an accurate time base.
To set the clock to the proper time:
1. Press when the LCD is displaying the clock.
2. The display shows, hh:mm, where ‘hh’ is the current hour and ‘mm’ is the current
minute. The first hours digit begins to blink, indicating that is the current digit to
set.
3. Press the pad to decrement the hours digit or press to increment the digit.
Since this is a 24-hour setting, the digits cycle through 0 > 1 > 2 > 0... .
4. When the correct digit is shown, press to save it. The current digit stops
blinking and the next digit begins to blink.
5. Repeat Steps 2 through 4 for each of the remaining digits until the display is
showing the correct time.
Note that there is no back key to return to a previous digit. If you make an error after
pressing the key, you have to start over.
2.2.2 Sigma-Delta A/D Demo
This section demonstrates the Sigma-Delta A/D Converter. For more information on
this module and its feature set, refer to the “PIC24F Family Reference Manual”, “16-Bit
Sigma-Delta A/D Converter” (DS30687).
Pressing the pad from the clock demo causes the LCD to momentarily display,
“SD ADC CH:DATA”. “CH:DATA” is the display format of the A/D result, where “CH” is
the Sigma-Delta A/D channel and “DATA” is a 16-bit signed hexadecimal value. Positive
values are in the range of 0000h to 7FFFh. Due to a slight offset voltage, the display may
indicate a small negative voltage (FFC0h to FFFFh). If the CH+/CH- inputs are
swapped, the display will show negative values (a range of 8000h to 0000h).
The demo uses CH1 to read an externally applied voltage with SV
DD (3.3V) as the A/D
voltage reference. The precision 2.5V reference can be used if the demo application is
modified (or replaced with custom code) to use CH1+ as the reference and
measurements are taken with the CH0 channel.
The input amplifier for the Sigma-Delta A/D is differential; that is, you can apply a
differential voltage across the two inputs. This is why swapping the inputs in the demo
generates a negative value. The amplifier has different gain settings but in the demo, it
is set for a gain of 1.
It is also possible to make a single-ended measurement with the Sigma-Delta A/D
Converter by applying a voltage to one terminal, while the other is the ground reference.
To do this, with using SV
DD as a reference:
1. Set jumper, J9, to the CH1+ position.
2. Connect an external jumper wire between CH1- (J7, Pin 23) and AV
SS (any of
the GND pins on J7).
3. Connect the voltage to be measured to CH1+ (J7, Pin 22). The voltage must be
in the range of 0V to 3.3V.