58MX 420 Installation and Service ManualThe external alarm is derived from the “ALARMout” port on cable (A) pin 18 (Black/White - ALARMout). The software is setup in each of the appropriate CFG1 (Alarms)menu. The relay coil supply voltage must be connected to an independent batterybacked-up alarm supply. Make sure the relay coil voltage is compatible with thevoltage rating of the alarm power supply (i.e. NTE Electronics Relay - P/N R14-11D10-12 for use in a 12 VDC supply). The negative ground of the alarm power supply mustbe connected to the “GND. to MX421” shield wire in Cable A (refer to the relay diagrambelow).CoilC N.O.N.C.Cable APin 18ALARMoutContinuous-DutySPDT Relay(12 VDC < 75 mA)MX 420To a Battery Back-UpAlarm Power Supply- +Cable APin 1 (Shield)(Gnd. To Mx421)Port 2: RS- 422 / RS- 232 Serial InterfaceThe CDU has a standard RS- 232 interface (similar to a PC COM). The RS-232 use thesame internal UART logic as the NMEA port 2. The TxD RS- 232 output and the NMEA2out RS- 422 output carries the same serial data, but with the electrical levels of eachstandard. The input is shared, and can only be set up to either receive RS- 232 inputor NMEA RS- 422 input.
