TRF7970A SPI Mode issues

user4300350

Other Parts Discussed in Thread: TRF7970A, TMS320F28376D

Hi there,

We are using the TMS320F28376D to communicate with the TRF7970A. The problem is we don't seem to be able to get the NFC driver to respond to any command we are sending. We played around with different configurations (changing clock polarity, clock frequency) without success.

Below are screen capture of the SPI signals and schematic. As you can see, the MISO line is not transitioning. I read some of the previous postings on the same subject, and checked with our FW team to ensure we are addressing the driver properly.

Any insight into possible solutions to this issue is welcome.

ch1: CLK

ch2: MOSI

ch3: MISO

ch4: SS

over 9 years ago

0 Josh Wyatt over 9 years ago

TI__Guru* 91206 points

you have tied VDD_I/O to 3.3V and I/O_1 and I/O_2 to VDD_X.
these three (VDD_I/O, I/O_1 and 2) should be on same rail, for starters.

what frequency is the SPI clock?

0 user4300350 over 9 years ago in reply to Josh Wyatt

Intellectual 310 points

Is there a power sequencing requirement between VDD_IO, VDD_X ? What can go wrong if i'm supplying VDD_I/O with an external 3.3V while using the internal regulator VDD_X to supply I/O_1 and I/O_2.
That being said, i'll fly wire VDD_X to VDD_I/O and see whether that'll make a difference.

Thanks

0 Josh Wyatt over 9 years ago in reply to user4300350

TI__Guru* 91206 points

all the digital I/O lines and VDD_I/O should be on same voltage rail.

0 user4300350 over 9 years ago in reply to Josh Wyatt

Intellectual 310 points

Josh Wyatt i went ahead and put my digital I/O lines and VDD_I/O on the same voltage rail (VDD_X) and it works.

Just a bit curious, can you explain a bit why this is required ?

Thanks

0 Josh Wyatt over 9 years ago in reply to user4300350

TI__Guru* 91206 points

the I/O voltage needs to be same for entire digital block, this is why.

Other wireless

Other wireless technologies forum

TRF7970A SPI Mode issues