Abstract
External signal are frequently analog in nature, requiring inter-conversion between analog and digital domains.
The interface between the digital nature of the processor and peripheral analog devices for the PIC18 core is the subject of this chapter. Coverage includes a comparison and characterization of digital and analog signals, digital-to-analog (DAC) and analog-to-digital (ADC) techniques. Architecture, configuration and electrical considerations for the 10-bit ADC module as well as the Analog Comparator and Voltage Reference modules are discussed. Also covered is the interface to proprietary DAC devices to generate analog signals.
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Notes
- 1.
Shannon, C.E.: Communication in the Presence of Noise, Proc. IRE, vol. 37, January 1949, pp. 10–21.
- 2.
Also the PIC24/30/32 families and some PIC16 devices.
- 3.
In the PIC18FXXK20 series, this is replaced by the FVRST (Fixed Voltage Reference STable bit in CVRCON2[6]. CVRCON2[7] holds the FVREN bit to enable this facility.
- 4.
There is a small uncertainty range in this difference signal of ±10 mV maximum (±5 mV typical) due to Comparator offset voltages.
- 5.
However, note that the Comparator module for this device is somewhat more flexible, with a several control registers to give the required options. For instance, each comparator has its own interrupt flag.
- 6.
For instance the PIC24H family.
- 7.
18- and 24-pin devices, lacking a Port E have up to 10 possible analog input channels.
- 8.
Early PIC16 device ADC modules use one AD Result register to hold one 8-bit outcome.
- 9.
For instance, the PIC18F1X20 use ADCON1 to individually enable each of the seven available analog inputs, and as a consequence the two VCFG bits move to ADCON0. The PIC18FXXK20 group use the two ANSELH:ANSEL registers to configure each of the 13 channels individually.
- 10.
In the PIC18FXXK20 channel 15 is also special, connected to the FVR—see Fig. 14.6.
- 11.
A conversion may be aborted at any time by clearing \(\mathsf{GO}/\overline{\mathsf{DONE}}\).
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Katzen, S. (2010). Take the Rough with the Smooth. In: The Essential PIC18® Microcontroller. Computer Communications and Networks. Springer, London. https://doi.org/10.1007/978-1-84996-229-2_14
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DOI: https://doi.org/10.1007/978-1-84996-229-2_14
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