AD5292 AD5293 Internal Shift Register Content After SYNC Went High

Hi,

With the AD5292 and AD5293 a high edge on _SYNC either has the chip consider the bits in the shift register as command or data, or it has the chip consider that edge as a PSI reset, if the number of clock edges was no multiple of 16.

What happens with the values in the shift register after that or at/before the _SYNC goes low again?

If I daisy chain ten AD5292 and want to only talk to the first five, can I then just clock in the 80 bits for the first 5 devices and raise _SYNC in order to let the 5 chips output their data, and do this several times?

Like after _SYNC goes high (and the data is considered or not, depending on the clock cont being a multiple of 16), are the shift register bits reset, or do the values keep stored and are used by the last five chips, if I only clock 80 new data bits in the next time again?

Regards,

Gerd



Typo in title
[edited by: GerdF at 1:21 PM (GMT 0) on 23 Apr 2020]
    •  Analog Employees 
    on Apr 24, 2020 9:47 AM 3 months ago

    Hi,

    Someone is currently looking into your query and will respond as soon as possible.

    Cheers,

    Ivan

    •  Analog Employees 
    on Apr 27, 2020 4:34 AM 3 months ago

    If the clock edges are not multiple of 16, then the write or read sequence relevant to the partial sequence will be ignored, as soon as the /SYNC goes high. Only the valid read or write sequences having 16 bits or its multiples will be accepted.

    Yes, in daisy chain, you can talk to the first five by clocking in 80 bits.

    Data coming out on SDO lines will act as the command sequence to the SDI of the next part. Serial register data do not get reset on /SYNC going high. Your purpose to retain previous serial register data to act as command to next device will not work in all cases.

    What will come out on SDO line in the next frame is decided by the command sequence provided in the current frame for the same part.

    If you look at Table 11 in the AD5293 DS, then the read commands will change the SDO data contents in the next frame.

    There is an example Table 09 to explain the same clearly.

  • "Serial register data do not get reset on /SYNC going high."

    Ok, that's what I needed to know. Many thanks!

    Although, my purpose was not to reuse the data for the first 5 ICs on the second five ICs, but I had hoped that the serial shift register would be reset to all zeros, so that I could have always just delivered 80 fresh bits in order to write to the first five ICs, and only cared about the second five ICs if I would have wanted to write to them.

    As the shift register is not reset on /SYNC going high, I will have to provide 80 zeros first (NOP for the second five ICs), followed by  80 relevant data bits (for the first 5 ICs) and then deassert /SYNC.

    Or I use a GPIO pin to either mask the /SYNC signal for the second five ICs or to switch on and off the pull-up line for the SDO pull-up resistors connected to ICs 4-9.

    •  Analog Employees 
    on Apr 28, 2020 4:09 AM 3 months ago in reply to GerdF

    Yes, you will have to provide 5 NOPs for the second set of 5 ICs followed by 5 commands for the first set of 5 ICs if configured in daisy chain.

  • With all the commands, DB15 and DB14 are meant to be 0. What happens if one or both of them are 1 ?

    Does the command associated with DB0 to DB13 get executed anyway (then there shouldn't be 0s but rather Xs), is the sequence ignored (just like with the NOP command) or is the behavior unspecified and therefore dangerous?

    I would like to put another IC on the same daisy chain as the AD5292s and might have to write to this other IC quite often. If the AD5292 would ignore any command not having two 0s as DB15 and DB14, I could just dispense with first clocking like 160 zeros into the chain but only use the 16 bits for the other IC, at least if that 16 bit word has DB15 or DB16 set to 1.

    Still another question regarding the AD5292 SPI interface:

    Figure 53 shows the digital feedthrough. Is this with a full active command transferred (presumably during the short peak up to 32µV) followed by the command taking place (taking about 5 to 7µs), or would such a peak be the result of a simple input line (like SCLK or DIN) toggle?

    If the former would be the case, do you have data on digital feedthrough with an NOP command or with the toggling of /SYNC, SCLK or DIN?

    Like if the analog circuitry would be adequately shielded from SCLK or DIN transitions at least if /SYNC of that particular IC is held high.

    And last but not least: Does ADI have an affordable GPIO IC that is compatible with the SPI daisy chain system used by the AD5292? I seem to be a little blind at the moment.
    I found something I could use in the MAX7317, but firstly it has the opposite CLK polarity and secondly it would be the only non-ADI IC on the board and why not go full-ADI if it would be possible...