What does the MI HMI expansion pod give me?

The expansion pod attaches to a midrange MI HMI. It gives two extra
comms ports, which may be used to run protocols, or accessed by
scripting. It increases the logging capability to 500 alarms and 500
events. If attached to an older A Revision unit, it provided battery
backup for internal data. B Revision units already have a battery backup
facility.