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ADS1118 followed by ISO7241C reads always 0XFF

Ankit Kumar
Prodigy 160 points
Other Parts Discussed in Thread: ISO7241C, ADS1118, ISO7241M

Dear Sir,

I am using ADS1118 and to isolate the SPI port, i have used ISO7241C. 

When i read data on MISO pin after ISO7241C, i always read 0xFF.  

Is it due to the wrong isolator used because ISO7241C has TTL input thresholds?

Please guide me?

should i have used ISO7241M?

I also suspect that whatever i am sending to ADC is going as 0xFF due to ISO7241C...Am i right?

Please help?

  • 0
    TI__Mastermind 28265 points

    Ankit,

    there can be many small causes why the interface is not working. The minimum SCLK-period of the ADS1118 is 250ns which results a 4MHz clock. The ISO7241C is a 25Mbps (12.5MHz) device. So the isolator is NOT too slow.

    1) When staring a data transfer you must at first pull the chip-select of the ADC low so it can read any information your are sending or activate its output for sending data to the ccontroller. Then you apply SCLK and send or receive data. Also the ISO7241 has two enable pins, EN1 and EN2, both of which must be pulled high to enable the output drivers.

     2) please also check that the ADC is configured correctly via DIN.

    3) please also check that the thermocouple you are using is working correctly. Simply apply some heat and check whether the output voltage of the thermocouple (mV-range) is changing from its initial value.

    4) If you have done this and it still does not work please send a schemtic and scope shots of your interface. Without seeing what you have designed I cannot guess or suggest any further actions.

    Regards, Thomas.