The ML500D™ has application in a wide variety of locations, fixed or mobile, to instantly provide up to five lines of voice telephone service. Each ML500D™ module has rear panel jacks for a Telco line and the local PBX/Phone so that calls may be received or placed over a Telco landline or the cellular network. Each ML500D™ module has a SLIC circuit to provide loop current and ring voltage to the PBX/Phone port when placing or receiving calls over the cellular network. Either the Telco line or Cellular network can be configured as the primary calling port.

If no calls are active, incoming calls from the Telco line or Cellular network will be connected through to the PBX/Phone port. However, if a call is active, an incoming call on the other port is ignored. Outgoing calls are placed through the primary line with the other line being used as backup. A line loss sensor monitors status of the Telco line and the internal processor monitors status of the cellular network.

Front panel LEDs indicate operating status and two push button switches are used to reset alarms and select the Telco line or Cellular network as the primary path for outgoing calls. Signal strength and cellular network status is available through the Program port. The SIM card socket is accessible by removing the module from the chassis. Alarm contacts on the rear panel can be used to monitor fail conditions. The ML500D™ may be ordered for 120Vac, 220Vac or 48Vdc power input.