The SIEMENS Model MMB-3 board in each MXL System controls operations and monitors input device identity, network communication, and operator commands that are entered through the MKB Annunciator/ Keyboard. The MMB-3 also provides two analog loop driver circuits. Each ALD-2I loop can be used as Class B or Class A and can monitor and control up to 60 intelligent devices as well as programmable device relays. The MMB-3 module can be programmed and upgraded in the field. It is equipped with two programmable Class B (Style Y) or Class A (Style Z) notification appliance circuits. Each circuit can activate up to 1.5 amps of audible or visual notification appliances. The MMB-3 has a user-defined Style 4 or Style 7 MNET communication port.