DM300019 datasheet(33/50 Pages) MICROCHIP

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Demonstration Program Operation

DS51584B-page 29

3.4.3

Digital-to-Analog Conversion

This program uses Digital Potentiometer MCP41010 on the dsPICDEM 80-Pin Starter

Development Board as a D/A converter to generate a sine-wave signal (audio tone) to

the LINE OUT pin. The digital potentiometer is driven by the output of the serial

peripheral interface SPI2 of the dsPIC30F6014A device, which receives its input from

the program.

The program retrieves HEX values from a table in data memory and delivers it to the

SPI. Thirty-two stored values cover the full range of the digital potentiometer. As the

analog output of the digital potentiometer passes through the MCP6022 Operational

Amplifier (configured as a low-pass filter) it results in a 400 Hz sine wave based on a

new table value every 125

μsec covering all 32 table values. The sine wave is placed

on the LINE OUT pin of the development board.

Figure 3-3 illustrates the digital-to-analog conversion process. Switches S1 and S2 are

used to change the output frequency to 800 Hz and 1600 Hz, respectively, by skipping

over some of the table values.

FIGURE 3-3:

DIGITAL-TO-ANALOG CONVERSION PROGRAM FLOW

INIT SPI2

Set W4 = Value Pointed to by

W1 Using PSV

Transmit Contents of W4 to

SPI2

Yes

Set Reg W2 to Start of Tone Table

Set Reg W3 to End of Tone Table

Set Reg W1 = W2

Has 150

μsec Interrupt

Occurred?

Set W1 = W1 + 2

S1 Pressed?

S2 Pressed?

Set W1 = W1 + 2

Set W1 = W1 + 4

Set W1 = W2

Yes

W1 > W3?

START

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