Your Udamonic computer has a multi-channel 12-bit Analog to Digital Converter (ADC).
Pins 1, 2, 3, 5, 6, 10, 11 can be assigned as analog inputs. The input voltage range is 0V to 3.3V.
Note: The datasheet for the PIC24FJ64GB202 processor indicates that RB15/AN9 (pin 12 on your Udamonic computer) is an analog input. This is an error on the datasheet, as RB15 is not available as an analog input on the PIC24FJ64GB202. See the Microchip Errata Sheet for more details.
Sampling an Analog Input
The word adc12 will configure the ADC for 12-bit sampling, while adc10 will configure it for 10-bit sampling.
The word analog will configure a pin to be an analog input. The format is pin analog. For example, to make pin 2 an analog input:
2 analog
To sample that analog input, first it must be selected as the current channel:
2 channel
Then the word sample performs the conversion and returns the result to the stack:
sample
In addition to the input channels, channel 29 will sample the negative reference voltage AVss (GND) and channel 30 will select the positive reference voltage, AVcc (3.3V).
29 channel
sample
will return 0 to the stack, while
30 channel
sample
will return 4096.
Setting the Conversion Clock
The ADC uses the system clock (Tcy) as the source for its conversion clock. On your Scamp, Tcy = 62.5 ns.
The word adcclk can be used to change the number of Tcy cycles used by the ADC. adcclk takes an 8-bit value from the stack (0..255). The conversion clock is equal to Tcy multiplied by this value plus 1.
The word adcclk can be used to change the number of Tcy cycles used by the ADC. adcclk takes an 8-bit value from the stack (0..255). The conversion clock is equal to Tcy multiplied by this value plus 1.
TAD = (n * TCY) + 1
For example, to make the conversion clock equal to 100 Tcy cycles:
#99 adcclk
The default setting for the conversion clock is 10, giving a conversion clock of 11 Tcy cycles (or 687.5 ns). On reset, the conversion clock resets back to 11 Tcy cycles. If you require a different setting, this should be configured in your initalization code. Note that a low value (fast conversion clock) may not give your ADC sufficient time to complete a conversion. The appropriate value depends on your application. For most simple applications, the default setting is fine.
Learn : Interfacing : Analog Input