The FPLMN (Forbidden Public Land Mobile Network) list is a collection of data stored on your SIM that consists of forbidden networks.
Warning: Clearing the FPLMN should only be done manually and when instructed by a member of the Hologram team.
Hologram does not normally recommend clearing the Permanent Forbidden PLMN List stored inside the EF file system in the SIM for two reasons:
- If the operation is performed while the module is scanning/attaching to a network, it can interrupt and restart that process on some modules resulting in unnecessary over-signaling.
- If the firmware clears this list frequently and is spinning in a loop, then that can result in excessive signaling through excessive retries to the same operator.
Adding forbidden networks
Traditionally, modems append networks to this list after failed attempts at registering onto them in order to speed up connections in the future. In order to determine if you have anything written on your FPLMN we recommend you run the following AT command:
Check the FPLMN
at+crsm=176,28539,0,0,12
We are telling the SIM to give us datafile 28539 in binary. Notice from the picture below that we get 24 "F"s this lets us know that the FPLMN is empty which is what we want. If you have anything other than 24 "F"s, then something has been written onto your FPLMN.
Removing forbidden networks
To clear the FPLMN, first consult your modem's documentation to make sure you are aware of any special instructions.
Usually you'll need to set the modem to minimal operation mode or airplane mode depending upon the module. In this example, we are setting the device to minimum functionality which disables transmit and receive RF circuits for both circuit switched and packet switched services with at+cfun=0.
Clear the FPLMN
at+crsm=214,28539,0,0,12,"FFFFFFFFFFFFFFFFFFFFFFFF"
Important: Be sure to include exactly 24 "F"s.
Lastly, don't forget to switch your device back to full functionality if that was modified.