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BQ78350-R1: How can I transfer informations between two masters via SMBUS?

Paul K52
Intellectual 640 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76920, BQ78350

Hello

Im working with the bq78350-r1, which is already a master in the smbus. I would like to transfer the information from the bq78350-r1 to another microcontroller via SMBUS.

But I think that the microcontroller is also a master.

What can I do?

  • 0
    TI__Guru 54715 points
    Hi Paul,
    The bq78350-R1 SMBus is normally read by a host device or master such as a MCU. Study the MCU specifications for its peripheral and the SMBus standards for how bus negotiation works.
  • 0 in reply to WM5295
    Intellectual 640 points

    Refering to the datasheet of the BQ78350-R1 on page 12 the BQ78350-R1 acts as a slave device on the SMBUS.

    So I can connect another microcontroller as a master to the SMBUS.

    In this configuration I could transfer the Information of the bq78350-R1 to the microcontroller.

    But the BQ78350-R1 is the host device for the BQ76920.

    Is that correct? Would this work?

  • 0 in reply to Paul K52
    TI__Guru 54715 points
    Hi Paul,
    Yes
  • 0 in reply to WM5295
    Intellectual 640 points
    But the device has also the ability to configure the charging algorithm to another charging IC via Smbus.
    So the chip can also act as a master because it can control an charging IC, right?
  • 0 in reply to Paul K52
    TI__Guru 54715 points

    Hi Paul,

    Yes, the bq78350 has broadcast mode available.  It becomes master to broadcast.  See the brief description in the technical reference manual.  Also see the SMBus specification and the SBS specification.  You might like section 1.2.2 of the SMBus Made Simple application note available in the bq78350-R1 product folder technical documents tab.

  • 0 in reply to WM5295
    Intellectual 640 points

    I read in the "Smbus made simple" that it can send Alarms and charging voltage and charging current. What about the other Information such as temperature, cell voltages ? Can this kind of information also be sent through the SMBUS to another microcontroller?

  • 0 in reply to Paul K52
    TI__Guru 54715 points
    Hi Paul,
    Read the bq78350-R1 technical reference manual. Charging information can be broadcast, most information must be read by the external host.
  • 0 in reply to WM5295
    Intellectual 640 points

    Ok I see in the technical refernce document on page 114 that there are commands, which can give me information about the measured voltage, current and temperature. These commands are called: ManufactuarerAcess() 0x0059 AFEConfig and MancufacturerAccess() 0x005A AFVCx

    I want to understand more in detail how the process will be to get the information, which I need:

    Q0: So I can access these commands from a microcontroller (master), which is connected to the BQ78350-R1 via smbus. If yes, I think I will need a library, where these commands are declared, right? Where can I find a library? Obivously otherwise I would get errors, because the compiler do not know what the SBS commands are about.

    Q1: By executing these commands the measured information will be sent from the BQ78350-R1 to a microcontroller (to a MSP430-Microcontroller for example)
    These informations will only be broadcast from the bq78350-R1, when the microcontroller will request the information via the commands, correct?
    In this case the BQ78350-R1 is the slave in this bus.

    Q2: Refering to the SMBUS made simple document on page 5, it is said that broadcasting should be avoided. This means that I the bq78350-R1 should not broadcast information about charging voltage and charging current, because during broadcasting the bq78350-r1 becomes master in the smbus and this is not good because a master conflict with the microcontroller (which is normally the master) can occur, right? 

    Q3: So, the best way would be to disable broadcasting mode from the BQ78350-R1. And execute commands from a microcontroller (master) to get the information which is needed.

    I would not get conflicts, and I would have a stable bus configuration: The Microcontroller is always the master of the smbus, and the bq78350-r1 is always the slave of the smbus, right?

    Thanks for making this clear

  • 0 in reply to WM5295
    Intellectual 640 points
    Hm, okay.
    And what about the library?
  • 0 in reply to Paul K52
    TI__Guru 54715 points
    Hi Paul,
    Check with your MCU supplier