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MCP3002 ADC chip, SPI questions

Topic last updated 01 Mar 2012, by Sebastian T. 0 replies
Sebastian T
01 Mar 2012

Hi,

I'm trying to get a ADC chip with SPI inteface running but I'm new to SPI and I'm running into some problems. A timing diagram can be seen below:

/media/uploads/s1000rr/adc.jpg

I set up the SPI interface to:

    spi.format(8,3);
    spi.frequency(1000000);
    signal = 2; //analog pin 18 on mbed
    cs = 1;
    cs = 0;

Based on the timing diagram, should I do the following:

    spi.write(0xFF);  //command to setup the chip assuming 
                      //assuming that it's correct

    int whoami = spi.write(0x00);
    pc.printf("WHOAMI register = %d\n\r", whoami);  
    whoami = spi.write(0x00);
    pc.printf("WHOAMI register = %d\n\n\r", whoami);

Or should I do:

    spi.write(0xFF);  //command to setup the chip assuming 
                      //assuming that it's correct

    int whoami = spi.write(0x00);
    pc.printf("WHOAMI register = %d\n\r", whoami);  

    spi.write(0xFF);  //command to setup the chip assuming 

    whoami = spi.write(0x00);
    pc.printf("WHOAMI register = %d\n\n\r", whoami);

The first version of the code will display 2 integers but they do not seem to be consistent. They might be ball park close for 2-5 times and then another set of numbers appears. The second version of the code outputs a "0" for the second pc.printf statement so I'm not sure on it. I'll go over my wiring again tomorrow and post a diagram, but if anyone has any suggestions than it would be greatly appreciated.

Thanks Sebastian