CATEGORY : PROGRAMMABLE MESSAGE DISPLAYS VFD (Vacuum Fluorescent Display), Character-based message displays A Message Controller is functionally the same product as the corresponding Master Message Display, except it has no display of its own. Thus, a Message Controller, like Master Message Display, stores messages and sends these messages to Slave Message Displays or Slave Marquees (to one, group, or broadcast), based on PLC and/or PC command. PMD Message Controllers include the PMD 180MC, PMD 370MC, and PMD 375MC Models.