It is not possible to use the Automation Server port log to view BACnet MS/TP communication
As of version 1.7 the BACnet plugin does not support logging MS/TP traffic to the com port's log file
Note that if an attempt is made to start logging on a port configured for BACnet MS/TP no indication is given that the operation is not supported. The log file is actually created but nothing is logged to the file.
At the time of this writing no information was available about if/when this functionality maybe will be added.