DPS310 CS, driven by GCM4, is fussy.

Please tell us which board you are using.
For CircuitPython issues, ask in the Adafruit CircuitPython forum.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
gollin
 
Posts: 1
Joined: Mon Apr 16, 2018 1:44 pm

DPS310 CS, driven by GCM4, is fussy.

Post by gollin »

Good morning!

I am driving a DPS310 SPI CS input with a digital pin from a Grand Central M4. The parts are on a breadboard that also includes an LSM9DS1, which communicates with the GCM4 via SPI.

The LSM9DS1 works fine-- I can drive its accelerometer/gyro CS pin from any digital GCM4 pin I've tried, without problem.

But the DPS310 is much fussier! Some GCM4 pins work fine with it (22, 23, 24, 25, 26, 27, 29, 40 are OK) but some do not (17, 28, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42). I don't find any clues in the variant.h file that might explain this behavior. I've looked at whether or not the LSM9DS1 CS line works with about half of these troublesome pins and find that it behaves just fine.

I note that the LSM9DS1 uses SPI_MODE3 while the DPS310 uses SPI_MODE0. I have no idea if that matters.

When I drive these two breakouts from a Feather M4 Express I do not see any signs of CS problems.

So here's what I did. Keeping in mind that the world is really analogue, and that I fixed a TTL look-ahead carry glitch years ago by loading the offending pin with a few pF cap, I put a 50 pF cap on the DPS310 CS pin. That fixed the problem.

So why'd I do this? It's 'cause I laid out a largish PCB loaded with breakout boards driven by a GCM4 and, to my irritation, found that the DPS310 on the board won't do SPI. So I've been drilling down, trying to understand the origin of the problem. I haven't yet put a scope probe on the CS pin to look at edge speeds, but it's easy enough to patch a small cap into the PCB, with a small modification in the next version.

Let me know if you'd like more information, or code, please.

George Gollin
[email protected]

Locked
Please be positive and constructive with your questions and comments.

Return to “Metro, Metro Express, and Grand Central Boards”