Hello,
I’ve inherited a legacy design that’s been in production in our company for many years. I’m presently troubleshooting a problem that’s been observed occasionally over the years.
The symptom is, after a power cycle, sometimes the host micro isn’t able to communicate with our DIGI CONNECT ME module (DC-ME4-01T-C). Also, in those states, we’re not able to ping the digi module with a TCP/IP client.
I noticed the reset pin is fed by a ULN2003LV that has open collector outputs.
I also noticed, that in the “Digi Device Customization and Itegration Guide” (doc num 90000734_A), shows an example circuit with a 10k pull up on the RESET line. This would imply there is no internal pull up inside the digi module.
The top side of the following image is our circuit. The bottom side of the image is the Digi example circuit regarding the reset line:
As you can see above, our design does not have the pullup.
Does the DC-ME4-01T-C RESET pin have an internal pull up to guarantee a non-reset state? Or, is this a potential design flaw on our end that might explain our intermittent behavior?
Thank you.