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[FAQ] ADS131A04: READY response word

Part Number: ADS131A04
Other Parts Discussed in Thread: ADS131A02

The data sheet for ADS131A0x states that the device responds with the READY word after reset: 0xFF02 for ADS131A02 and 0xFF04 for ADS131A04. However, if I send multiple NULL command frames, the response received in the first frame is incorrect while the subsequent responses are correct. Why is the READY response incorrect in the first frame after reset?

  • This is expected behavior. The device is ready to accept commands when the power-on cycle is completed and the SPI responds with a READY status word. However, when the host first communicates with the ADS131A0x after power-up, the SPI interface requires one SCLK pulse to wake up. This will cause one extra bit to shift out of the DOUT pin and the received READY word will appear shifted one bit to the right.

    For example, in the ADS131A04, the expected response is 0xFF04, so a shift of one bit to the right will yield the response 0xFF82. For the ADS131A02, the expected response is 0xFF02, so a shift of one bit to the right will yield the response 0xFF81.

    To start communications after power-up, send the NULL command in back-to-back frames and the expected READY response will be received in the second frame.