Analog Devices ADC Application Notes

a ADSP-21990: Utilization of the Analog to Digital Converter (ADC) AN21990-05

ADSP-21990: Utilization of the

Analog to Digital Converter (ADC)

AN21990-05

a ADSP-21990: Utilization of the Analog to Digital Converter (ADC) AN21990-05

Table of Contents

SUMMARY...................................................................................................................... 3

1 IMPLEMENTATION OF THE ADC LIBRARY ROUTINE......................................... 3

1.1 Usage of ADC routine ....................................................................................................................................3

1.2 Usage of DSP registers ...................................................................................................................................3

1.3 Configuring the ADC block...........................................................................................................................4

1.3.1 adc.h .............................................................................................................................................................4

1.3.2 adc.dsp .........................................................................................................................................................4

2 SOFTWARE EXAMPLE: UTILIZATION OF THE ADC BLOCK TO GENERATE

THREE-PHASE SINE-WAVE PWM................................................................................ 4

2.1 Main.dsp..........................................................................................................................................................4

2.2 Main.h..............................................................................................................................................................5

3 EXPERIMENTAL RESULTS.................................................................................... 5

a ADSP-21990: Utilization of the Analog to Digital Converter (ADC) AN21990-05

Summary

This application note demonstrates the usage of the pipeline flash Analog to Digital Converter (ADC) system

on the ADSP-21990. Section one will discuss the ADC library routines. In section two, an example will be used to demonstrate the usage of these routines. The last section shows some experimental results.

1 Implementation of the ADC library routine

1.1 Usage of ADC routine

In this library, two routines are defined for initialising the ADC block and reading the ADC channel values. It is developed as an easy-to-use library, which has to be linked to the user’s application. The library consists of two files. The file “adc.dsp” contains the assembly code of the subroutines. The block has to be compiled and then linked to an application. The user has to include the header file “adc.h”, which provides the function-like call to the subroutine. The following table shows the macro that is defined in this library.

Operation Usage Explanation

Initialisation

Read ADC

ADC_Init(ADC_Number_of_samples, ADC_EOC_interrupt_label)

ADC_Read(ADC_DATAX, Offset_0to3 or Offset_4to7)

Initialise the ADC block, including configuring the ADC end of conversion interrupt

Reading the ADC channel values, with the offset values being taken into account

Table 1 Implementation Routine

This routine requires a configuration constant from the main include-file “main.h” that comes with every application note. Section 2 shows an example of usage of this library. For more information regarding this routine, see the comments in the “adc.h” and the “adc.dsp” files.

1.2 Usage of DSP registers

The macro listed in the Table 1 is based on the subroutine listed in Table 2. This subroutine will be discussed in the following section. The following table gives an overview of what DSP registers are used in this macro:

Subroutine Inputs

ADC_Init_

ADC_Scale_

Table 2 Input and output format, modified registers in the ADC library routines

ADC_Number_of_samples: the number of samples to be taken for calculating the offset

None

Outputs Modified registers

mr1 = Offset_0to3

sr1 = Offset_4to7

ar = ADC channel value after offset

ar, ay0, ay1, mr, mx0, my0, sr,

ar, ay0

Please refer to the ADSP-21990 hardware reference manual for information on the ADC block

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