This one:
PCI Express® Mini Card Electromechanical Specification Revision 2.1
members.pcisig.com/wg/PCI-SIG/d … load/10031
- for the second SIM, the standard defines no pins, so Sierra had to deviate to provide the additional signals
- Sierra just loves to repurpose signals defined by the standard and making the card unworkable in a standard compliant slot. Happened to us multiple times we had to redesign a board because the module would not work at all or we were risking hardware damage - 1.8V reference on PCIe clock line, really?