Difference between revisions of "ADC Using PIC16F877A"

 
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In this tutorial we are going to discuss how to use the inbuilt PIC16f877A ADC.<br>
 
In this tutorial we are going to discuss how to use the inbuilt PIC16f877A ADC.<br>
 
We will be reading the ADC values from chanel Zero and transmitted on UART at 9600 baudrate.
 
We will be reading the ADC values from chanel Zero and transmitted on UART at 9600 baudrate.
−
[[FILE:Lpc1768Adc.gif]]
+
[[FILE:ADC.gif]]
 
<br><br>
 
<br><br>
  
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=PIC16F877A ADC pins=
 
=PIC16F877A ADC pins=
−
PIC16F877A has inbuilt 8channel 10-bit ADC. Below tables shows the ADC pin mapping.<br>
+
PIC16F877A has an inbuilt 10 bit Successive Approximation ADC which is multiplexed among 8 input pins.<br>
 +
The A/D module has high and low-voltage reference input that is software selectable to some combination of VDD, VSS, RA2 or RA3.
 +
With 5v as the Vref the resolution of Pic16f877a ADC can be determined as below:
 +
$$resolution of ADC = Vref/(2^{10}-1) = 5/1023 =0.004887 = 4.887mv$$
 +
 
 +
The below table shows the ADC input pins multiplexed with other GPIO pins.<br>
 +
The ADC pin can be enabled by configuring the corresponding ACON1 register.<br>
 +
When the ADC function is selected for a pin ,then other Digital signals are disconnected from the ADC input pins.
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
{| class="table table-striped table-hover table-condensed table-bordered"
 
|-class="info"
 
|-class="info"
 
!Adc Channel || Pic16f877a Pin || Pin Function  
 
!Adc Channel || Pic16f877a Pin || Pin Function  
 
|-
 
|-
−
|0|| PA.0 || AN0
+
|0|| RA0 || AN0
 
|-         
 
|-         
−
|1|| PA.1 || AN1
+
|1|| RA1 || AN1
 
|-         
 
|-         
−
|2|| PA.2 || AN2/VREF-
+
|2|| RA2 || AN2/VREF-
 
|-         
 
|-         
−
|3|| PA.3 || AN3/VREF+
+
|3|| RA3 || AN3/VREF+
 
|-             
 
|-             
−
|4|| PA.5 || AN4
+
|4|| RA5 || AN4
 
|-         
 
|-         
−
|2|| PE.0 || AN5
+
|2|| RE0 || AN5
 
|-         
 
|-         
−
|3|| PE.1 || AN6
+
|3|| RE1 || AN6
 
|-           
 
|-           
−
|4|| PE.2 || AN7
+
|4|| RE2 || AN7
 
|}<br><br>
 
|}<br><br>
  
 +
=ADC Registers=
 +
The below table shows the registers associated with PIC16F877A ADC.<br>
 +
{| class="table table-striped table-hover table-condensed table-bordered"
 +
|-class="info"
 +
!Register || Description
 +
|-
 +
|ADCON0|| Used to Turn ON the ADC, Select the Sampling Freq and also Start the conversion.
 +
|-
 +
|ADCON1|| Used to configure the gpio pins for ADC
 +
|-
 +
|ADRESH|| Holds the higher byte of ADC result
 +
|-
 +
|ADRESL|| Holds the lower byte of ADC result
 +
|}
 +
<br><br>
  
 +
Now lets see how to configure the individual registers for UART communication.
 +
{| class="table table-striped table-hover table-condensed table-bordered"
 +
|-class="info"
 +
|ADCON0
 +
|-
 +
|7 || 6 ||  5 || 4 || 3 || 2 || 1 || 0 
 +
|-
 +
|ADCS1 || ADCS0 || CHS2 || CHS1 || CHS0 || GO/DONE || — || ADON
 +
|}
 +
<b>ADCS2-ADCS0:</b>A/D Conversion Clock Select bits
 +
[[FILE:adc_Freq_Select.png]]
  
 +
<b>CHS2-CHS0:</b>Analog Channel Select bits<br>
 +
000 = Channel 0 (AN0)<br>
 +
001 = Channel 1 (AN1)<br>
 +
010 = Channel 2 (AN2)<br>
 +
011 = Channel 3 (AN3)<br>
 +
100 = Channel 4 (AN4)<br>
 +
101 = Channel 5 (AN5)<br>
 +
110 = Channel 6 (AN6)<br>
 +
111 = Channel 7 (AN7)
  
 +
<b>GO/DONE:</b> A/D Conversion Status bit<br>
 +
When ADON = 1:<br>
 +
1 = A/D conversion in progress (setting this bit starts the A/D conversion which is automatically cleared by hardware when the A/D conversion is complete)<br>
 +
0 = A/D conversion not in progress
  
 +
<b>ADON:</b> A/D On bit<br>
 +
1 = A/D converter module is powered up<br>
 +
0 = A/D converter module is shut-off and consumes no operating current
 +
 +
 +
{| class="table table-striped table-hover table-condensed table-bordered"
 +
|-class="info"
 +
|ADCON1
 +
|-
 +
|7 || 6 ||  5 || 4 || 3 || 2 || 1 || 0 
 +
|-
 +
|ADFM || ADCS2 || — || — || PCFG3 || PCFG2 || PCFG1 || PCFG0
 +
|}
 +
<b>ADFM:</b> A/D Result Format Select bit<br>
 +
1 = Right justified. Six (6) Most Significant bits of ADRESH are read as ‘0’.<br>
 +
0 = Left justified. Six (6) Least Significant bits of ADRESL are read as ‘0’.
 +
[[FILE:Adc_Result_Justification.png]]
 +
 +
<b>ADCS2:</b> A/D Conversion Clock Select bit<br>
 +
Check ADCS1:ADCS0 of ADCON0 register.
 +
 +
<b>PCFG3-PCFG0:</b> A/D Port Configuration Control bits
 +
[[FILE:Adc_pin_config.png]]
 +
<br><br>
 +
 +
[[FILE:PicAdcBlockDiagram.png]]
 +
 +
=Hardware Connections=
 +
[[File:ADCExample bb.png|none]]
  
 
=Code=
 
=Code=
−
Below is the sample code to read the ADC value of channel0 and sent it on UART at 9600 baud rate.<br>
+
Below is the sample code to read the ADC value of channel0 and send it on UART at 9600 baud rate.<br>
−
As the POT is connected to ADC0, the values can be varied using this POT.
+
<html>
 +
<script src="https://gist.github.com/SaheblalBagwan/051cc0daca8d1cafcf662449a5fe271a.js"></script>
 +
</html>
 +
 
 +
=Using ExploreEmbedded Libraries=
 
<html>
 
<html>
 
<script src="https://gist.github.com/sharanago/83a7537783383c8130576a79a493c87a.js"></script>
 
<script src="https://gist.github.com/sharanago/83a7537783383c8130576a79a493c87a.js"></script>
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[[File:Pic16f877aADC01.PNG]]<br><br>
 
[[File:Pic16f877aADC01.PNG]]<br><br>
 +
 +
=Downloads=
 +
Download the complete project folder from the below link:<br>
 +
[https://github.com/ExploreEmbedded/Pic16f877a_ExploreUltraPicDevKit/archive/master.zip Hardware design Files and Code Library]
 +
 +
 +
Have a opinion, suggestion , question or feedback about the article let it out here!
 +
{{DISQUS}}

Latest revision as of 11:17, 24 May 2016

In this tutorial we are going to discuss how to use the inbuilt PIC16f877A ADC.
We will be reading the ADC values from chanel Zero and transmitted on UART at 9600 baudrate. ADC.gif


PIC16F877A ADC pins

PIC16F877A has an inbuilt 10 bit Successive Approximation ADC which is multiplexed among 8 input pins.
The A/D module has high and low-voltage reference input that is software selectable to some combination of VDD, VSS, RA2 or RA3. With 5v as the Vref the resolution of Pic16f877a ADC can be determined as below: $$resolution of ADC = Vref/(2^{10}-1) = 5/1023 =0.004887 = 4.887mv$$

The below table shows the ADC input pins multiplexed with other GPIO pins.
The ADC pin can be enabled by configuring the corresponding ACON1 register.
When the ADC function is selected for a pin ,then other Digital signals are disconnected from the ADC input pins.

Adc Channel Pic16f877a Pin Pin Function
0 RA0 AN0
1 RA1 AN1
2 RA2 AN2/VREF-
3 RA3 AN3/VREF+
4 RA5 AN4
2 RE0 AN5
3 RE1 AN6
4 RE2 AN7


ADC Registers

The below table shows the registers associated with PIC16F877A ADC.

Register Description
ADCON0 Used to Turn ON the ADC, Select the Sampling Freq and also Start the conversion.
ADCON1 Used to configure the gpio pins for ADC
ADRESH Holds the higher byte of ADC result
ADRESL Holds the lower byte of ADC result



Now lets see how to configure the individual registers for UART communication.

ADCON0
7 6 5 4 3 2 1 0
ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE — ADON

ADCS2-ADCS0:A/D Conversion Clock Select bits Adc Freq Select.png

CHS2-CHS0:Analog Channel Select bits
000 = Channel 0 (AN0)
001 = Channel 1 (AN1)
010 = Channel 2 (AN2)
011 = Channel 3 (AN3)
100 = Channel 4 (AN4)
101 = Channel 5 (AN5)
110 = Channel 6 (AN6)
111 = Channel 7 (AN7)

GO/DONE: A/D Conversion Status bit
When ADON = 1:
1 = A/D conversion in progress (setting this bit starts the A/D conversion which is automatically cleared by hardware when the A/D conversion is complete)
0 = A/D conversion not in progress

ADON: A/D On bit
1 = A/D converter module is powered up
0 = A/D converter module is shut-off and consumes no operating current


ADCON1
7 6 5 4 3 2 1 0
ADFM ADCS2 — — PCFG3 PCFG2 PCFG1 PCFG0

ADFM: A/D Result Format Select bit
1 = Right justified. Six (6) Most Significant bits of ADRESH are read as ‘0’.
0 = Left justified. Six (6) Least Significant bits of ADRESL are read as ‘0’. Adc Result Justification.png

ADCS2: A/D Conversion Clock Select bit
Check ADCS1:ADCS0 of ADCON0 register.

PCFG3-PCFG0: A/D Port Configuration Control bits Adc pin config.png

PicAdcBlockDiagram.png

Hardware Connections

ADCExample bb.png

Code

Below is the sample code to read the ADC value of channel0 and send it on UART at 9600 baud rate.

Using ExploreEmbedded Libraries

Pic16f877aADC01.PNG

Downloads

Download the complete project folder from the below link:
Hardware design Files and Code Library


Have a opinion, suggestion , question or feedback about the article let it out here!

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