SPI - SDO long tail

[YChen.41]

Hello,

I am having problems with STM32C8T6 interfacing with TI ADS8317.

1. Long tail at SDO line (first & second image)
2. The seperation time between each byte is always significantly long (not sure if this is a problem) ( second image)

Second image is the enlargement of the first.

The code responsable for this is simply:

 HAL_SPI_Receive(&hspi1, tempADCdata, 3, 1); //tempADCdata

The setting is as follow:

SPI: Full Duplex Master

Bit rate: 6 Mbits/s

CPOL: 0

CPHA: 0 (rising edge)

Could you kindly point me to potential solution to solve the above issues?

Best

Danny

[waclawek.jan]

> STM32C8T6

Which one is that, exactly?

> Long tail at SDO line (first & second image)

I assume you are talking about MISO line.

Why would that be a problem? There are no clocks during that time, so nothing is read.

You can try to switch on a pullup on the MISO line.

> The seperation time between each byte is always significantly long (not sure if this is a problem)

It's you who can judge if it's a problem. The ADC appears to have a relatively wide tolerance for clock, so as long as the longest period (i.e. adding the inter-character gap) converts to above the lowest allowed clock frequency, it should be OK. But I personally would try to avoid it.

Don't use Cube, write your own routine to send/receive. Use higher compiler optimization settings.

JW

[Uwe Bonnes]

It seems the line is tristated.