How to work with inbuilt ADC Module of PIC18F4550

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A microcontroller, a digital device, can read, execute and transmit only digital signals. On the contrary, the outputs of the most of the transducers are analog in nature. Thus it is hard to interface these transducers directly with controllers. Analog-to-digital convertor (ADC) ICs are one way to make the analog input compatible with the microcontroller.

Using an external ADC adds complexity to the circuit. To avoid this complexity, PIC Microcontrollers have in-built ADC module which reduces the cost and connections of the circuit. This article explains the in-built ADC of PIC18F4550 controller.

As mentioned in the summary, a PIC microcontroller has inbuilt ADC for A/D conversion. The ADC module of PIC18F4550 controller has following specifications:

· 10-bit resolution output which means that an analog input gets converted into a corresponding 10-bit digital output.

· 13 channels which means that a total of 13 analog signals can be converted simultaneously into digital.

· Vref+ (RA3) and Vref- (RA2) pins for external reference voltage.

· 8 selectable clock options.

· ADC can be in auto-triggering mode for continuous A/D conversion.

ADC Registers:

To work with the inbuilt ADC of this PIC microcontroller, the certain registers are required to be configured. Each of these ADC registers has been explained below.

1. ADCON0 (A/D CONTROL REGISTER 0)

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
—	—	CHS3	CHS2	CHS1	CHS0	GO/DONE	ADON

ADON: This bit is used to enable/disable the ADC peripheral of the PIC.

1 = A/D converter module is enabled

0 = A/D converter module is disabled

GO/DONE: This is A/D conversion status bit. For ADON=1,

1 = A/D conversion in progress

0 = A/D Idle

CHS3: CHS0: These bits are used to select a particular analog channel from 13 available channels (0-12) which are multiplexed with digital I/O pins. The following table shows the bit configuration to select these analog channels:

CHS3:CHS0	Analog Channel	Pin
0000	Channel 0	RA0/AN0
0001	Channel 1	RA1/AN1
0010	Channel 2	RA2/AN2
0011	Channel 3	RA3/AN3
0100	Channel 4	RA5/AN4
0101	Channel 5	RE0/AN5
0110	Channel 6	RE1/AN6
0111	Channel 7	RE2/AN7
1000	Channel 8	RB2/AN8
1001	Channel 9	RB3/AN9
1010	Channel 10	RB1/AN10
1011	Channel 11	RB4/AN11
1100	Channel 12	RB0/AN12

2. ADCON1 (A/D CONTROL REGISTER 1)

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
—	—	VCFG1	VCFG0	PCFG3	PCFG2	PCFG1	PCFG0

PCFG0:PCFG3: As mentioned earlier, there are 13 analog channels in PIC18F4550 which are multiplexed with digital I/O pins. This means that such a (multiplexed) pin can act as either a digital I/O pin or an analog input pin. Either of these configurations is selected by these bits. The following table shows the bit configuration to make a pin D (Digital I/O) or A (Analog input):

For more detail: How to work with inbuilt ADC Module of PIC18F4550

About The Author

Ibrar Ayyub

I am an experienced technical writer with a Master's degree in computer science from BZU Multan University. I have written for various industries, mainly home automation, and engineering. I have a clear and simple writing style and am skilled in using infographics and diagrams. I am a great researcher and is able to present information in a well-organized and logical manner.

Categories: Projects, Sensor - Transducer - Detector Projects, Tutorials
Tags: adc module, pic18f4550