BQ79731-Q1: Can not write to the DIAG_ADC_CTRL1 [VF_GP_THR] register

Hi Christoph,

I ran a quick test in the lab and the functionality of this register is working. Can you try running these commands on a different device? What does your setup look like?

Best,

Zachary

Hi Zachary!

Thank you for your quick reply. I have used a different device and get the same problem. 

The BQ is used on our own PCB and communicates via UART with an STM32H7 chip (MCU). The BQ is used as a base device (there are no other stack devices). I have sent you a screenshot of the UART communication. First, the BQ is woken up with a 2.3ms long wake-up ping. After that I wait 10ms before starting the communication (this is not shown in the screenshot). Then I start the auto-addressing. For the sake of simplicity, after auto addressing I immediately send the command where I write the value 0x01 to DIAG_ADC_CTRL1 [VF_GP_THR] --> register 0x315 (0xD0; 0x03; 0x15; 0x01; 0x07; 0xB4). Then I send the command to read out register 0x315 (0xC0; 0x03; 0x15; 0x00; 0xC2; 0xB4). The BQ responds with 0x00; 0x00; 0x03; 0x15; 0x00; 0xDA; 0x90. The value in the register is 0x00 and not 0x01, so the previous command to write to the register was ignored. Do I have to do anything before I can write on this register?

BR, Christoph

Hi Zachary!

I repeated the test with the Evalboard BQ79731Q1EVM-060 and the behavior is the same. In the screenshot you can see that I write the value 1 to register 0x315. When I read out the register, the value 0 is in the register. Obviously I cannot write directly to the register. What am I doing wrong here? Do I need to do anything else first? Can you help me with my problem?

BR, Christoph

Hi Christopher,

I will do more testing on my side. In the meantime, are you able to test with the GUI and a USB2ANY?

Best,

Zachary

Hi Zachary!

Unfortunately, I cannot work with the GUI or USB2ANYBUS -> My MCU (STM32H7) communicates via UART.

BR, Christoph

Christoph,

Have you had communication issues with anything else? You send your command immediately after auto-addressing, can you try adding a 100uS delay after your auto-address sequence, and then send write command?

Best,

Zachary

Sorry, try 100mS, not uS.

Hi Zachary!

I waited 100ms. The behavior is the same.

BR, Christoph

Hi Christoph,

Okay, are you able to send any other write command and read back to see if you have any communication with the device? For example, try writing to the customer registers and reading them back. You can try CUST_MISC1 which is register 0x015.

Best,

Zachary

Hi Zachary!

I can write to register 0x15 and also read it out (see image). I have written the value 0x02 in the register 0x15 and when I read out the register, I also get this value. In your first answer you wrote "I ran a quick test in the lab and the functionality of this register is working". I need the UART commands on how to write to the register 0x315 correctly! -> All commands after the wakeup ping.

BR, Christoph

HI Zachary!

Do you have any new information for me yet?

BR, Christoph

Hi Cristoph,

See if you can write to the register before and write 2 bytes to encompass your target register. And then read 2 bytes from the register before and see if this works.

Best,

Zachary

Hi!

If you had looked at the operating manual, you would have seen that register 0x314 (register before DIAG_ADC_CTRL1) is reserved. It cannot be written to! Writing to the register 0x315 (DIAG_ADC_CTRL1) obviously works for you -> Send me all UART commands (after wakeup ping) on how to write to the register correctly!!!!

BR

Christoph,

The register doesn't latch which isn't made clear in the datasheet. Thats why you are reading back 0. However, the register still works and I am able to successfully complete a GPIO analog path check. The steps needed to do so are in the datasheet.

Zachary