LMP90100: SPI Data Read issue, LSB not reading correctly, even after using chip select between the two transactions

Tiago Furtado

Part Number: LMP90100

Tool/software:

The problem I am having is exactly the one reported in this thread.

However the marked solution has not resolved the problem. I am still missing the the LSB, and the nature of that issue is no different if I use CS between the two transaction of a read or none. The original example code for MSP430 in snac029.zip also does not assert CS between the two transactions either.

The waveform for 0x13 is actually falling at the same time that SCK is rising.

Are there any other possible solutions I could try?

9 months ago

0 Angel Rodriguez de San Miguel Bermudez 9 months ago

TI__Expert 8130 points

Hi Tiago,

Can you provide the logic analyzer captures of your digital communication when doing a data read?

The following post show's an example of an adc conversion data read with the LMP90100: (+) [FAQ] LMP90100: Reading data from the LMP90100 registers - Data converters forum - Data converters - TI E2E support forums

Does your SPI transaction follow the same format as shown in the digital communication captures here?

Best Regards,

Angel

+1 Tiago Furtado 9 months ago in reply to Angel Rodriguez de San Miguel Bermudez

Prodigy 150 points

Thank you for the response. I don't have any captures, but looking at the oscilloscope output showed exactly the same waveforms as presented in the thread I referenced.

However, seemingly I have resolved the issue. I'll state what resolved it, in case others stumble upon this thread.

Asserting a CS for each transaction did not resolve the issue. What resolved the issue is Writing 1 to SW_OFF_TRG in SPI_HANDSHAKECN resolved the problem. According to the datasheet the effect of this is thus :

1: SDO’s high-Z is postponed to the subsequent falling edge following the last (16th, 24th, 32nd, etc) rising edge of SCLK. This option provides additional hold time for the last bit, DB0, in nonstreaming read transfers.

I have not yet tested streaming read transfers. I'll update this thread if I run into issues there.

I have tested streaming reads and writes and they function as expected

0 Angel Rodriguez de San Miguel Bermudez 9 months ago in reply to Tiago Furtado

TI__Expert 8130 points

Hi Tiago,

Thanks for sharing what resolved your issue. Feel free to reach out if you run into any additional questions.

Best Regards,

Angel