• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 611 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ76920: how to “not use” RESERVED bits

Xun
Mastermind 18121 points
Other Parts Discussed in Thread: BQ76920

Dear team,

customer SLAT is developing the SW on the host micro that is connected to the BQ76920 on his board.

 

Looking at the register map in the datasheet, it seems there are many RESERVED bits, that the programmer “shall not use”.

 

2 question:

·         Why does the DS mention several different comments for the RESERVED bits ?

Examples:

Reserved. Do not use

These bits are for TI internal debug use only and must be configured to the default settings indicated

·         These bits are acessed though the I²C interface.

But how to “not use” some RESERVED bits since the host MCU will execute 8-bit access to the registers of the BQ76920 through I²C ?

  • 0
    TI__Guru 54715 points

    Some reserved register bits have no function, some do have a function which could alter the performance of the device.This may account for some of the differences in notes on the bits.  The datasheet also evolved over some period of time, different authors or different mindsets of the author at different times may have contributed to some of the differences.

    Generally the reserved bits should not be changed from default settings.  The settings can be read from the device after boot, or are shown in the datasheet tables.  A developer may want to confirm both.  While the developer may want to access the registers with a read/modify/write process, it is recommended that the reserved bits always be written to their default value so that if some erroneous transaction were to set a reserved bit, a subsequent write would fix it rather than prolong the wrong setting.

    In earlier datasheets the register 8 bit 3 was incorrectly shown with a reset value of "1".  The default value is 0 and should not be changed for proper operation. Customers who coded from the datasheet and set this bit found the current trip thresholds were lower than expected. Be sure the customer uses the latest datasheet.

  • 0 in reply to WM5295
    TI__Mastermind 18121 points
    Thanks a lot Willy!