We are trying to use the AD5700 evaluation board to achieve bi-directional communication through HART between an MCU and a PC.
The MCU is connected to the AD5700 through UART (1200, 8o1). Sending data from the PC through our HART adaptor works fine.
The correct UART data reaches the MCU. However, when the MCU responds on UART, the data does not get through to the PC.
The connections:
    - MCU TX as output for AD5700 TX
    - MCU RX as input for the AD5700 RX
    - MCU CD reads AD5700 CD and only sends when CD is 0
    - MCU RTS as input for AD5700 RTS and only sends after it sets RTS to low (idle is high)
The behavior (jumpers are default.) which we get in full-duplex AD5700 mode:
    - While AD5700 is waiting, CD is low; if we send HART data from the PC, it becomes high and the data reaches the MCU through UART
    - After the complete HART frame is received through UART, the MCU sets RTS high and starts sending, but the PC receives nothing
In half-duplex, CD is always high and some data reaches the MCU through UART, but it is not the correct frame; the MCU then does not respond.
Parents Reply
  • Hello,

    I am one of Loredana's colleagues and am working with her on the proiect.

    The correct connections are TX-TX and RX-RX according to the official documents. Initially we used TX-RX and RX-TX, because this is was made sense, but after a day of debugging we figured out the names are switched on the AD5700 evaluation board.

    See the attached image, taken from this document: https://www.analog.com/media/en/technical-documentation/data-sheets/AD5700_5700-1.pdf. It labels TXD as data input and RXD as data output.

    The modulator's output is HART OUT and the demodulator input is HART IN, according to Figure 1 in the document.

    If we connect TX-RX; RX-TX we get nothing on the UART lines. We sniff them with a couple of USB converters. However, if we use TX-TX and RX-RX the MCU receives UART messages and it responds to them.

    Thank you,


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