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There have been big warnings all over the place for the last several versions saying not to use bypass mode. Yet, despite that, the newest firmware actually includes a new command specifically for adjusting the underlying baud rate while working in bypass mode so we’re definitely not the only ones still using it.
I’m reading and testing more and I’m not so sure that I want to be setting the profile to “1/No Profile/SIM ICCID selected” for a Hologram SIM. While in the part of the documentation for the carrier profile command Digi says to use “1” for no configuration if you’re not connecting, in the steps of the connection process, they recommend this setting for European customers but not Americans. u-blox doesn’t provide any clarity at all on what the different profiles are. When Digi is describing the commands to manually select an LTE bands, they specify that bands can only be manually selected if the carrier profile is set to “1/No Profile.” So I started testing going back and forth between the different profiles using both the Digi commands (CP0-3) and the u-blox commands (UMNOPROF) and using both a Hologram SIM and the T-Mobile SIM I yanked out of my own cell phone. When I use my T-Mobile SIM, setting the carrier profile to either “1/None” in the XBee firmware or setting the UMNOPROF to “1/SIM ICCID select” does indeed make it “figure it out” and on the next reset if I query the profile the response is 5/T-Mobile. The Digi firmware doesn’t apparently doesn’t handle any CP response except 0/1/2/3 so it continues to report “1” but the u-blox has definitely locked on to T-Mobile. But, when using a Hologram SIM, the same magic doesn’t happen. The module can’t figure out what the profile for the SIM should be so it leaves it as whatever it was last selected to be. I was beginning to think that the command was just not working because I couldn’t ever get a response of 1 back to the “UMNOPROF?” command or see any change from it at all until I put in the T-Mobile SIM and saw that it go automatically to 5 after a request of 1. When left in transparent through a couple of resets and setting CP=1, it Digi sets the u-blox profile to 100=standard Europe. I’m strongly suspect that the u-blox “standard European” profile might actually mean “open up all the bands and either manually select the ones you really want or hope your SIM picks one” since Digi specifies that you must use CP=1 if you do want to manually select and u-blox says that selecting a profile will over-write all manual band selection. I’m just not so sure I trust the Hologram SIM to really stay connected when left to its own devices like that. I got most of the boards that had refused to connect to connect again by setting CP to 1, but I don’t know if the success was because I picked 1 or because I changed it at all. After all, all the boards I was messing with were boards that had previously connected and stayed connected for few weeks or months using no carrier profile at all. I think going forward I would prefer to specifically select the AT&T profile unless I know the board will be deployed somewhere with no AT&T signal.
