M-bus 01.03.2020 09:21 04.03.2020 17:53

The SX-1181 module is designed for the connection of up to 64 devices equipped with an M-Bus (ČSN EN 1434) - usually heat meters, etc. The mechanical design is suitable for the installation on the U-rail ČSN EN 60715. The module is equipped with fixed screw terminals and it is designed to be connected to the serial port RS-232 of the Foxtrot basic module. The M-Bus interface is terminated in the screw terminal block.

The M-bus interface is powered by 24 VDC/30-150 mA. The consumption depends on the number of devices connected. The RS-232 interface and the M-Bus are galvanically separated with a 1 kV isolation voltage.


An example of connection of the module to the Foxtrot basic module is shown in the following figure. The SX-1181 module is connected to the serial channel CH1 with the RS-232 interface. If the modules are not placed next to each other, a shielded cable must be used. The M-Bus interface may be powered from the same source, if the heat meters do not need to be galvanically isolated. Otherwise, this part can be powered from a separate power supply.


Fig. 1. Connecting the SX-1181 module to the CH1 interface of the CP-1004 module



  1. Up to 64 meters can be connected to the SX-1181 module, which implies a maximum quiescent current in the bus at 96mA, and the total consumption of the module max. 150 mA.

  2. A standard maximum length of the cable (the M-Bus) is 350 m; if a maximum line resistance < 30 is observed, as well as a maximum capacity 0.82μF (maximum rate of 9,600 baud, recommended rate 2,400 baud), the total length of the line can be up to 4 km.

  3. The recommended cable is a standard telephone type, with the 0.8mm diameter, better shielded (shielding should be connected on the side of the SX-1181 module to the protective earth PE). It is also recommended to use the J-Y(St)Y 1x2x0.8 cable.

  4. The SX-1181 module is a device of the "modem" type, and it is also connected correspondingly: the TxD terminal on the SX-1181 should also be connected to the same TxD signal on the Foxtrot basic module; analogy, this also applies to the RxD and RTS (the signals do not interfere!)

  5. The GND1 (B3, B4) and GND (A1, A2, A3) terminals are galvanically isolated. If the module is powered from a separate source (connected to the terminals + 24V and GND1), the GND terminal must be connected to the RS232 of the basic module (the terminal of the signal ground of the RS-232 interface in the basic module).