BMS Slaves Test Setup about bms-fw

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General Notes from the Datasheet

• The LTC6811 has two variants, LTC6811-1 and LTC6811-2. We are using LTC6811-1.
• Each LTC6811 has 12 cell-sensing inputs. If we have 96 cell banks to measure, we need 8 of these chips.
• The LTC6811-1 allows for "daisy chaining" where one chip's data is passed to the next, which then passes both its data and the data it recieved from the previous chip to the next chip, on and on until all every chip's data is passed to the BMS master at the end of the chain.
• There are many different measurement frequency modes for the LTC6811. The tradeoff made here is higher accuracy and less noise requires lower measurement frequency. The lowest frequency, most accurate measurement is 26Hz. This is still much faster than the sensor read task's frequency, so this mode seems best.
• Noise level for 26Hz is maximum 50µV peak-to-peak (16 bits ADC resolution). shutdown thresholds must take this into account.
• ADSTAT command measures internal device parameters and has a fault code. Use this in initial startup checks. ADSTATD does the same thing with "digital reduncancy"
• A watchdog timer resets the LTC6811 if it has not recieved a valid command for over two seconds. The WDT pin is internally pulled up when this happens

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SPI Interface Specification
Altium Schematic:https://americas-team-phantom-simon-fraser-university.365.altium.com/designs/7BDB24F0-FA72-44F9-A03A-2E26A19A2FF2?variant=[No+Variations]&activeDocumentId=BMS_SLAVE_SHEET.SchDoc#design

• LTC6811-1 can operate as an SPI master or slave. We only need it to behave as an SPI slave and we need the GPIO pins (which are used by SPI master mode) for thermistors.
• LTC6811-1 uses its own special communication protocol to pass information along the daisy chain. It is called isoSPI but it is not an SPI interface; it is a totally different protocol.
• According to the datasheet, isoSPI has very good magnetic noise isolation and reliability since it uses a two wire differential signal.
• isoSPI is only used for communication between LTC6811-1 chips in the daisy chain. A regular 4-pin (MOSI, MISO, CLK, CS) SPI interface is used to connect the chain to the BMS master.
• isoSPI always uses port B pins 45, 46, 47, 48 (IBIAS, ICMP, IMB, IPB respectively), but can also use port A pins 41, 42 (IMA, IPA respectively) if ISOMD pin is connected to Vreg. This connection is made in the Altium schematic.

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Questions for Faizan (BMS Slave PCB Designer)

1. 
   Why does the

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A new Accumulator Box team member was hired to replace Faizan, who is MIA. The new member was to take over development of the BMS slave PCBs. Through some discussions with Tractive System team, it was determined that the previous slave chip and board will work. BMS is switching back from the LTC6811 to the BQ76PL455A. The next step is to determine how much progress had been made on the BQ76PL455A firmware.