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BQ76PL455A-Q1: Query regards to Communication protocal

Vikram Jain
Intellectual 485 points
Part Number: BQ76PL455A-Q1

Dear All, 

I am currently working with BQ76PL455 evm and using it with TMS57LS04x launchpad. what i really want to understand is that when you have BQ devices connect in a daisy chain can you do all commands related to configuring the BQ stack devices like auto-addressing, AFE configuration, sampling, storing and reading as a broadcast message with and without response ? Or it needs to be polled individually itself ? 

The main architectural design challenge i am facing is to design a real time OS where the cycle round is 1 ms, and if you need to poll each devices connected in daisy chain individually for configuration then most of the time out of 1ms will be utilized by only BQ driver.

Or can we do group assign ? Not even sure how how grouping works. 

Your help shall be really appreciated

Regards

Vikram Jain 

  • 0
    TI__Genius 11480 points
    Hello Vikram,

    You can use a broadcast write to configure stacked devices. For the pl455 "with response" means a write and "without response" is synonymous with read. You can also assign by groups (using a base device as group 0 and stacked devices as group 1, for example).

    Many of the settings you mentioned can be written once in power up, or burned into EEPROM then checked at powerup and then most of your cycle time will be free for cell measurements/diagnostics etc.

    I think the example code and software design reference found on the technical documents page will be of use to you.
  • 0 in reply to David Wiest Jr
    Intellectual 485 points

    Hi David, thank you so much for your reply.

    I have gone through that tech document. But I think i might not be understanding it right, so say you have 'x' device stacked in the daisy chained and i want to read all cell voltages and aux input. So to do this can you actually do a broadcast msg without resp to sample and store the data and then individually poll each device to read data in chunks like read cell 1 to 5, then 6 to 10 then 11 to 15 then 1 to 4 aux and 5 to 8 aux ? Is it possible to do it like this ? ALso how the sampling would be don on this stage ? 

    Regards

    Vikram Jain

  • 0 in reply to Vikram Jain
    TI__Genius 11480 points
    Vikram,

    You are partially correct. You can do a broadcast sample & store. Then you can write again to the command register to do a "read stored values" command, and you will get back all of the ADC reads in one transaction from that particular device.

    The sampling is done by sending a "sample and store (or send) command" by writing to register 0x02. Depending on the command you send the ADC will store all of the values converted, or send all the values converted. What the ADC measures is configured in the CHANNELS register.

    I would caution you against attempting to poll cell voltages every ms. This will be quite challenging, if not impossible depending on the channels register and ADC configuration. It is common for us to see customers measure every 50-100ms. You may be able to do 10ms comfortably enough