UART protocol description doubt : BQ76PL455AQ1

Harsh Gugale

Other Parts Discussed in Thread: BQ76PL455A-Q1

Hello,

I am using BQ76PL455AQ1 for EV application.An algorithm to calculate CRC is given on Page 52 of the datasheet.It inverts respective byte in the frame appends these bytes and then calculates CRC using the method.Do we have to send each byte now as LSB first or MSB first since CRC was calculated for the inverted bytes.

For instance:

Can I pass 0x91,0x03etc directly in the UART with LSBFIRST?

over 7 years ago

0 Stephen Holland over 7 years ago

TI__Intellectual 2795 points

The UART data must be sent MSB-first.

0 Harsh Gugale over 7 years ago in reply to Stephen Holland

Prodigy 240 points

Thanks Stephen for your reply and sorry for the late response.

The BQ76PL455AQ1 that I am using is connected correctly as VP and VM both clamp to their respective voltages so I know that it can receive the command frame.I am using Freescale FRDM KL46z to communicate with the IC (that is the only MCU available with me right now I am providing 5V wakeup and VIO from the 5V supply available on the board).Firstly, please inform me if 3v3 UART is compatible with BQ76pl455AQ1.

If that is fine I am sending a command frame to read the digital die version number using the following frame :
0x80,0x00,0x00, + (2 CRC bytes)

Now, first I invert all these bytes since they have to be sent MSBFIRST as you had mentioned and the UART avaialable with me is LSBFIRST.But the chip doesn't respond.

Any help would be highly appreciated.
Thanks so much!

0 Stephen Holland over 7 years ago in reply to Harsh Gugale

TI__Intellectual 2795 points

Hi Harsh,

The UART can support 3.3V signals, however, it would be expected that VIO would also be attached to the same IOVCC supply of 3.3V.

A single device read of device address 0, register address 0, 1 data byte requested, would be 0x81, 0x00, 0x00, 0x00, + CRC.

I would strongly suggest reviewing the bq76PL455A-Q1 Software Design Reference document here: www.ti.com/.../technicaldocuments

0 Harsh Gugale over 7 years ago in reply to Stephen Holland

Prodigy 240 points

Hi Stephen,

Thank you for your response and suggestion.I realized my mistake in the frame and I am reading the manual thoroughly again.I gave VIO 3.3V as you had suggested but in contrary to the 5V VIO the VP this time did not clamp to 5.3V(It did give me 5.3V when I connected a 5V VIO).Any suggestions in this case?

Thanks,

Harsh