AT$LTC?
Read command provides the first 300 characters of each valid
certificate stored in NVM in the format:
$LTC: <string>,<total_message_length>,1,<security_object_type>
If no certificate is stored, the read command provides:
$LTC: "",0,1,<security_object_type>
AT$LTC=?
Test command returns the range of values for parameters
<total_message_length>, <seq_no> and <security_object_type>.