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AD5629R multiple byte operation

Hello all,

I have read in the datasheet of  AD5629R that setting bit DB22 to 0 means standard 3-byte and 4 byte mode. I am a little unclear how does this work. How to change between 3 and 4 byte mode ?

If i set this mode, I don't know how many bytes to send.

Thanks in advance,


  • Hi Adrian,
    By setting command 1001 in the command bits then writing 2 bytes of data continuously.
    This command used to enable 2 byte mode transfer.
    The 24-bit shift register will look like as follows :   24-Bit Input Shift Register
    DB0 = 0 = 2byte mode trnsfer is turned-off
    DB0 = 1 => 2byte mode transfer is turned-on
    After giving this command , the next command onwards 2 byte mode transfer will be enabled.
    Below would be the sequence for enabling 2 bye mode transfer..
    Repeat (Start – Address Byte – Command Byte – MSB Byte of Data – LSB Byte of Data Command Byte – Repeat (MSB Byte of Data – LSB Byte of Data)-Stop)   2 Byte Operation
    3 bytes marked in red enables the 2 byte mode transfer. Once this command is executed, 2 byte
    mode will be enabled from next command onwards.
  • Thank you very much Padraic,

    I understand now how to enable the 2 byte mode. I still am a bit unsure of how to use it. 

    I suppose the point in 2byte mode is to reduce overhead in communication.

    Now say I want to write as fast as possible to one dac output. How would I exploit the 2byte mode for maximizing speed to write to one dac?

    I am guessing here:

    Repeat (Start – Addr – Comd(2 Byte Mode) – MSB of Data – LSB of Data – Comd(wr dacN) – Repeat (MSB of Data – LSB of Data)-

    Comd(wr dacN) – Repeat (MSB of Data – LSB of Data),

    Comd(wr dacN) – Repeat (MSB of Data – LSB of Data), #etc,,,

    Stop)  ????

    Extending the problem to "How to write as fast as possible to a range of dac's in sequence". Could potentially be using the same protocol when N is changing from cycle to cycle.

    Hope for your ideas here, as I really think the datasheet is not up to date with this information


  • Hi  , 

    I suppose after enabling 2byte mode, only the first write would need a command byte, the succeeding would just be 2bytes for the MSbyte and LSByte. 

    Best regards,


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