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ADC Reference input pin selection issue

 
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Boyce



Joined: 07 Feb 2010
Posts: 39

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ADC Reference input pin selection issue
PostPosted: Tue Mar 09, 2010 12:34 am     Reply with quote
Compiler 4.104 16F690

I am trying to find a way to use one of the ADC input pins as a reference voltage input for the other ADC input pins. I don't see how to do it.

This did not work:
Code:

setup_adc_ports(sAN1|sAN2|sAN3|VSS_REF|sAN0);

This does work, but I need a different reference voltage:
Code:

setup_adc_ports(sAN1|sAN2|sAN3|VSS_REF);

How can I use the voltage reference I need to use, like two diode drops?

Thanks,
Boyce

Code:

This is from the 16F690.h file:

// Constants used in SETUP_ADC_PORTS() are:
#define sAN0            1       //| A0   \\!"K50"
#define sAN1            2       //| A1   \\!"K50"
#define sAN2            4       //| A2   \\!"K50"
#define sAN3            8       //| A4
#define sAN4            16      //| C0
#define sAN5            32      //| C1
#define sAN6            64      //| C2
#define sAN7            128     //| C3
#define sAN8         0x10000    //| C6
#define sAN9         0x20000    //| C7
#define sAN10        0x40000    //| B4
#define sAN11        0x80000    //| B5
#define NO_ANALOGS      0       // None
#define ALL_ANALOG   0xF00FF    // A0 A1 A2 A4 C0 C1 C2 C3 C6 C7 B4 B5

// One of the following may be OR'ed in with the above using |
#define VSS_VDD              0x0000        //| Range 0-Vdd
#define VSS_VREF             0x4000        //| Range 0-Vref

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