MC7421 module disappears from Windows device manager

IoT Modules
1

Hello.
We are testing MC7421 in our IoT gateways and have tested both with Linux and Windows IoT.
However it seems like the module, installed in an Mini PCIe socket inside the PC unit, only occasionally is registered at system boot (in device manager in Windows or with lsusb in Linux.

I notice from the datasheet, that this is mentioned related to Host Interface Pin Assignments:
Pin 22 - SYSTEM_RESET_N - note F
F: The module must not be plugged into a port that supports PCI Express. The pin is used by a PCIE signal, which can cause the module to be in reset state or occasionally reset.

What does this mean and could this be the reason, that we are experiencing very unstable registration of the modules? We have tested with several MC7421 modules and several PCs etc.

Is it possible that a firmware upgrade can fix the issues we have or can this behavior be changed in any way using AT commands for example?

Any help is much appreciated.

Thanks.
/Kevin

2

Hi @kevin1 ,
Welcome you to our community!
Could you please share with me some information as below:

  1. Have you installed the driver for your MC7421 module? If not, please install driver for MC7421 module by following the link below:

https://source.sierrawireless.com/resources/airprime/software/airprime-em_mc-series-windows-drivers-qmi-build-latest-release/#sthash.QE5ehqZ6.dpbs

Then try again, Do the issue still happens in this case?

  1. Are you using your MC7421 module on a Sierra board or a custom board?

Thanks,

3

Hi.

  1. Yes, we have installed the latest driver from the site you are linking to.
  2. We have not installed the Mini PCIe module on a Sierra board, but in an industrial PC of the brand CompuLab. Are there any limitations or something we should be aware of when using this particular Sierra Wireless MC7421 module on a typical PC board?

Br. Kevin

4

Hello again.
It seems like our issue is this:
Pin 22 - SYSTEM_RESET_N - note F
F: The module must not be plugged into a port that supports PCI Express. The pin is used by a PCIE signal, which can cause the module to be in reset state or occasionally reset.

Apparently our host PC / Mini PCIe socket sends a reset signal on pin 22. This is not an issue with other Mini PCIe modules, but apparently with MC7421.

So my question is if its possible to program this differently using AT commands or with an upgraded firmware?

Thanks.

Br. Kevin

5

Hi @kevin1 ,
Your issue is similar to below topic. Can you take a look and see if it helps you?

Thanks,

6

@jerdung
Thanks - I definitely think my issue is similar to this.
However I am not sure which pins to cover - any suggestion based on the pinout description table for MC7421?
Thanks,

7

Hi @kevin1,
According to the ticket I gave you for reference above, you have to cover the pins (23, 25, 31, 33) for the module to work.
Could you please try and see if that solves your issue?
You can refer to Section 2 - Electrical Specifications on page 19 in the link below for more details about MC7421 module Host Interface Pin Assignment:

Thanks,