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Labview with LTC6811 BMS Daisy Chain Issues

Category: Software
Product Number: ltc6811-1
Software Version: Labview 2019

Hi, im trying to build a BMS by using 2 ltc6811-1 boards and daisy chaining them together. I am confused as to how the isoSPI works. For the first board which is connected to my controller, i am using the 14-ribbon SPI. For the connection of the bottom board to the top board i am using the RJ45 cable provided. In my Labview program, i am unsure of how to wake up the second board. My current program is able to read up to 12 cells but I am looking to further expand its capabilities. From what i can understand, the isoSPI port takes 600us to wake up and be at the ready state. I would have to wake up the isoSPI port before sending the read configuration command? x0002. 

  • That is correct, the number of wakeup pulses you send should be at least the same as the number of the devices in the daisy-chain.  Once all the devices are woken up commands will propagate between devices automatically so commands only need to be sent once.  Data is then sent or received in device by device after the single command code is transmitted.

  • I appreciate your reply.Ok so if i have 2 devices connected, the commands that should be sent is first x0000 as a dummy bye ( to wake up isoSPI port) then wait 600us for it to be ready, then send x0002. Then send x0000 again and wait another 600us before sending another valid command. Am i right?

  • 2 devices as in 2ltc6811 daisy chain together

  • The order of bytes should be as follows: [Toggle CS, wait 600us, CMD1, CMD0, CPEC1, CPEC0, D0, D1, ..., Dx, DPEC0, DPEC1, D0, D1, ..., Dx, DPEC0, DPEC1]

    If a read command the red is data read from device 0, blue data read from device 1.  For more than two devices any further data read will be for the next device up the daisy chain.

    If a write command the same order applies but the red data sent first goes to device 1, the blue data to device 0.  Any further data sent will push the red data to the next device up the daisy-chain.

  • I am still having issues with my program. I have calculated my Twakeup time to be 0.008s as my serial communication frequency is 20kHz.  My current transition state is 1) Wake up IsoSPI 2) Read Config 3) Set Config 4) Start Cell 5) Read Group A 6) Read Group B 7) Read Group C 8) Read Group D 9) Clear Register. I came across a LTC6820. From what i understand it seems that its able to solve my isoSPI issue without me having to change my current program which was monitoring 12 cells before. Would buying a LTC6820 help me to solve my problem?