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18F4550 10 bit A/D with a Refrence Voltage

 
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adamgreg



Joined: 16 May 2008
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18F4550 10 bit A/D with a Refrence Voltage
PostPosted: Fri May 16, 2008 1:16 pm     Reply with quote
I can't seem to find how to setup a reference voltage for A/D on the 4550.
Looking through the 18F4550.h file there isn't any way to do it?

Anyone have any ideas?

--Adam
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Fri May 16, 2008 1:25 pm     Reply with quote
See this section in the .H file:
Code:
// The following may be OR'ed in with the above using |
#define VSS_VDD               0x00              // Range 0-Vdd
#define VREF_VREF             0x30              // Range VrefL-VrefH
#define VREF_VDD              0x20              // Range VrefL-Vdd
#define VSS_VREF              0x10              // Range 0-VrefH
adamgreg



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How do you specify which pin is the ref
PostPosted: Fri May 16, 2008 1:38 pm     Reply with quote
Alright so I want Pin_A1 to be the Analog input and I want Pin_A3 to be the reference pin. How do you specify which pin is the ref pin?
PCM programmer



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PostPosted: Fri May 16, 2008 1:56 pm     Reply with quote
The A/D reference voltage pins are always on AN3 and AN2.
To use AN1 for A/D input and to use AN3 for Vref+, do this:
Code:

setup_adc_ports(AN0_TO_AN3 | VSS_VREF);
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