I have a small linux SBC and I used 7304 and 7354 modems previously without any issues, but now I am upgrading them to use mc7455s and I noticed that they would not work at all. No USB enumeration, nothing, like the modules are not inserted in the mini-pcie slots.
Then comparing the 7304,7455 and the mini-pcie standard pinout, it seems that the 7455 might be breaking the standard.
pin 11,13 on the modem VREF_1.8 output and USIM2_PWR (3V) output. But pcie pinout shows refclk+/- there.
pin 23,25 on the modem is USB3TX+/- but the std has PERN/P.
pin 31,33 on the modem is USB3RX+/- but that is PETN/P on pcie.
These collisions were enough to stop the modem from working at all. As a test I have stuck small stripes of scotch tape to these pins and voila the modem is back.
Did I miss some sentence in the 7455’s technical spec that says: careful, might not be compatible with mini-pcie?
Any feedback is appreciated