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Original question:

ADS1220: Open thermocouple detection with ADS1220IPWR?

ADS1220: thermocouple temperature data read error

Ganesh Sivaramalingam
Prodigy 20 points
Part Number: ADS1220

Hi,

I'm working on the ADS1220 with STM32 integration through SPI interface. I'm trying to read thermocouple temp  like this

spi.select(mode1)  -> CS made as OUTPUT low  

spi.write(0x1F)  ->  (1F means RDATA command from ADS1220 data sheet)

I used below command to read buffer spi.Read(buff,0x03)

but my buff[0] always shows same value (0x35). 

so this value is not getting updated. Am I missing any configuration settings like IDAC current or IDAC routing?

  • 0
    TI__Guru** 113765 points

    Hi Ganesh,

    Welcome to the E2E forum! Can you send me your schematic and the device configuration that you are using?  I would make sure that the configuration you are writing to the ADS1220 is read back from the registers.  Can you also send me oscilloscope or logic analyzer shots of your communication?

    The ADS1220 uses byte transfers. You must make sure that you are sending and receiving the correct number of bytes and are reading the correct data.  The command is 1 byte, and the data is 3 bytes.  CS must stay low throughout the entire communication.  You should use a '0' for sending a null byte.  So as shown in the datasheet the RDATA command should be a total of 4 byte transfers of 0x10, 0x00, 0x00, 0x00.

    I don't know how the write and read functions work in your code.  Normally a write is required to transmit the required SCLKs.  The receive buffer would be filled as the device transmits.  To determine if your SPI is working with the code you are using requires that the signals be monitored with a scope or logic analyzer to make sure that the communication is correct.

    Also, the default mode for the ADS1220 is single-shot mode and requires that the START command be issued to start the conversion.

    A thermocouple is a self-powered source and does not require excitation.  I would suggest that you take a look at A Basic Guide to Thermocouple Measurements.

    Best regards,

    Bob B