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SPI Chip Select polarity

Added by David Bowden about 2 months ago

I have a SPI device which wants Chip Select to be inverted (low when not in use, high when in use) from "normal" usage. I don't think I'm supposed to share the entire datasheet, but here's a screenshot showing the expected CS level during communications. The device is an Infineon H-Bridge, BTM9021 (The datasheet is for the BTM9010/BTM9011).
Portion of datasheet showing intended Chip Select polarity

I do not see a way to invert the Chip Select signal during normal use, so I end up with the Chip Select inverted, get no MISO response, and cannot communicate with the chip.
Oscilloscope capture showing actual Chip Select polarity

I am aware that it should be possible to implement the Chip Select separately in software, but I haven't figured it out yet. I would appreciate any suggestions on how that could be accomplished.

I also note that polarity control for the SPI chip select doesn't appear to be supported in Waijung 2 either (at least I didn't see it in the documentation -- I haven't used Waijung 2 yet)

David

clipboard-202410080924-zwz1y.png View clipboard-202410080924-zwz1y.png 26 KB Portion of datasheet showing intended Chip Select polarity
clipboard-202410080925-q2agt.png View clipboard-202410080925-q2agt.png 72.6 KB Oscilloscope capture showing actual Chip Select polarity

Replies (4)

RE: SPI Chip Select polarity - Added by David Bowden about 2 months ago

Huh -- it looks like I have MOSI and MISO tags reversed on the scope capture above. I must not have been paying attention

RE: SPI Chip Select polarity - Added by Parth Maheshwari (พาร์ท) about 2 months ago

Hi David,

Just to confirm, is this issue resolved?

Sincere regards,
Parth

RE: SPI Chip Select polarity - Added by David Bowden 29 days ago

Sorry, I didn't actually expect an answer, so haven't checked back in recently!

The original issue I reported has not been resolved as far as I know, and it appears to be present in Waijung 2 as well (I'm not currently using Waijung 2, so can't confirm).

There is a workaround if you control the Chip Select line by other means, but I don't see a way to invert its state with the existing controls.

David

RE: SPI Chip Select polarity - Added by Chandima Jayaneththi (จันทิมา) 25 days ago

Hi David,

Unfortunately, we don't provide any official support for Waijung 1 anymore. Currently, Waijung 2 only supports active-high chip select signal. We will consider adding an option to select the active-high or active-low mode for the chip select pin for Waijung 2 in future releases.

Best regards,
Chandima.

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