SPI Chip Select polarity
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). 
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.
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
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Added by David Bowden 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
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Added by Parth Maheshwari (พาร์ท) 2 months ago
Hi David,
Just to confirm, is this issue resolved?
Sincere regards,
Parth
RE: SPI Chip Select polarity
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Added by David Bowden about 1 month 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
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Added by Chandima Jayaneththi (จันทิมา) about 1 month 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.