Analog I/O Wildcard User Guide

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To read a voltage from channel 2 (pin 12 on the Field Header) on module 1 with a single-ended conversion, use the function AD16_Sample as shown in the example code Listings 1-5 and
1-6.

Listing 1-5 C Code Listing for reading A/D Channel 2 on Module 1.

#include <\mosaic\allqed.h>	// include all qed utilities
#include "library.c"	// be sure to include kernel ext
#define ANALOG_MODULE1 1	// define current module
void main ( void )
{
uint ad16_result;
Init_Analog_IO(INT_2V_DAC12,ANALOG_MODULE1);	// init DAC to use 2.048 int ref
ad16_result = AD16_Sample( AD16_CH2, ANALOG_MODULE1 ); // read ch 2 on mod 1
printf("AD Result = %u\n",ad16_result);	// print out A/D counts
}

Listing 1-6 Forth Code Listing for reading A/D Channel 2 on Module 1.

DECIMAL	\ set base to decimal
1 CONSTANT ANALOG_MODULE1	\ define current module
INT_2V_DAC12 ANALOG_MODULE1 Init_Analog_IO	\ init DAC to use 2.048 internal ref
AD16_CH2 ANALOG_MODULE1 AD16_Sample	\ read sample from ch 2 on mod 1
U.	\ print out A/D counts

To convert the 16-bit result returned from AD16_Sample into a voltage, use Equation 1-2.

Input Voltage = +IN − −IN = ( Count / 65536 ) * Vref Eqn. 1-2

Vref in Equation 1-2 is the reference voltage selected using the voltage reference selection jumpers which were described in the section entitled "Selecting The Reference Voltage". With the default voltage reference selection jumper configuration (jumpers J4 and J6 installed), Vref is 4.096 volts.

Components and transducers with high output impedances connected to the analog inputs will introduce errors in the analog to digital converter. Table 1-7 shows the maximum source resistance at various sampling rates. Larger source resistances may cause conversion errors of more than one least significant bit (LSB).

The function AD16_Multiple rapidly obtains a specified number of samples from an A/D channel and stores the results as sequential 2-byte values in memory starting at the specified extended address. If the specified extended address is in common RAM, the fastest sampling frequency is approximately 17 kHz (corresponding to 57.5 microseconds per sample). If the specified extended address is in paged memory, the fastest sampling frequency is approximately 12 kHz (corresponding to 82.5 microseconds per sample). The timing parameter specifies the timing of the samples, with 0 representing the fastest sampling rate, and 65,535 representing the slowest sampling rate. See the glossary entry for more information.

Table 1-7 Maximum Source Resistance at Various Sampling Rates

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Analog I/O Wildcard User Guide