I observe this behavior with other MMC cards as well, but only with my new hardware. The CM4 modules are not new. Ok, you mentioned that newer MMC cards switch to 1.8V, but the problem is that the MMC is being powered with 3.3V. In this case, I would need to switch from 3.3V to 1.8V, but that's not accounted for in my layout.
What also stands out is that the voltage on the clock signal drops by about 10% after the 33-ohm resistor. Are the 33 ohms too high? The reference design didn't use series resistors. I added them mainly as a debugging tool to have a way to monitor the signals.
In the picture you can see the clock signal before the 33-ohm resistor, and in "clock2," you can see the signal after the resistor (the signal has dropped). Could the series resistor be too large and causing interference?
In the picture "cmd," you can see a severely attenuated CMD signal. In the picture "cmd1," you can see the CMD signal when no MMC is installed. I still don’t fully understand what’s happening here. However, the MMC is fine — it works in other devices. The CM4 module is also fine, as it works in other devices. I can't detect any short circuits or issues with the traces.
What also stands out is that the voltage on the clock signal drops by about 10% after the 33-ohm resistor. Are the 33 ohms too high? The reference design didn't use series resistors. I added them mainly as a debugging tool to have a way to monitor the signals.
In the picture you can see the clock signal before the 33-ohm resistor, and in "clock2," you can see the signal after the resistor (the signal has dropped). Could the series resistor be too large and causing interference?
In the picture "cmd," you can see a severely attenuated CMD signal. In the picture "cmd1," you can see the CMD signal when no MMC is installed. I still don’t fully understand what’s happening here. However, the MMC is fine — it works in other devices. The CM4 module is also fine, as it works in other devices. I can't detect any short circuits or issues with the traces.
Statistics: Posted by gs105 — Mon Dec 16, 2024 3:55 pm