MM20-X-GSM mala


Decode founded cooperation with KSB Group.

Cooperation is based on placement of MM20-GSM device, branded as DHC10.


  • Transparent and simultaneous readout of M-Bus slave devices and communication with devices on RS-485 line over GSM network
  • GPRS communication with control system
  • Readout up to 20 M-Bus slave devices
  • Short circuit protection of M-Bus line
  • Galvanic isolated M-Bus line up to 1kV DC
  • Conversion of Modbus TCP to Modbus RTU protocol at RS-485 port
  • RS-232 interface for local device setup
  • Remote device setup over SMS messages
  • Complete device state diagnostic over LED indications
  • Power supply 9-30V DC or 230V AC
  • 35mm DIN rail mounting


DHC10 is communication device intended for remote readout over GSM/GPRS connection:
– devices on M-Bus line with M-Bus protocol (heat, water, electric, gas meters...)
– devices on RS-485 line with transparent or Modbus RTU protocol (PLCs, I/O modules, pumps...)

M-Bus port is galvanically isolated and designed to withstand short circuit on M-Bus line. RS-485 port can be configured to convert Modbus TCP to Modbus RTU protocol. Device setup can be done locally or remotely over SMS messages. LED indications show device status and can be used for complete diagnostic. Depending on version, power supply is 9-30V DC or 230V AC. Device is prepared for 35mm DIN rail mounting and it is fully adjusted for industrial communications, automation processes and telemetry.


DHC10 acts on M-bus line as standard M-Bus master device which can sustain up to 20 M-Bus slave devices. Simultaneously with readout of M-Bus slave devices, it can communicate with devices on RS-485 line. GSM/GPRS communication is carried out via microcontroller controlled GSM module which enables one UDP server and one TCP server connection. M-Bus and RS-485 ports can be assigned to one of these connections. DHC10 is designed to work with fixed IP addresses in VPN (Virtual Private Network).
PC, over serial connection and GSM modem, or LAN connection and 2G/3G router, connects to GSM/GPRS VPN network. Client software sends UDP/TCP packets with requests for RS-485 and M-Bus devices. DHC10 converter extracts serial requests from UDP/TCP packets and sends it to RS-485 and M-Bus ports. Responses from serial ports are packed by DHC10 device in to UDP/TCP packets and sent back to client software.

MM20-GSM 200

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GSM module

SIMCom SIM900, Quad-band GSM/GPRS

GSM antenna connection

SMA jack

SIM card

Standard (1.8V/3.0V) SIM card

Remote connection

Over GPRS, one TCP/IP server, one UDP/IP server

Remote setup

Over SMS messages

Serial interface

Connection: RJ45
RS-232 DCE – device setup, firmware update
speed 115200bps, data format 8N1
RS-485 – transparent or Modbus RTU protocol
speed and data format adjustable for RS-485 interface

M-Bus interface

Connection: pluggable screw terminal, max 2.5mm2
M-Bus master – transparent protocol
up to 20 M-Bus slave devices
speed (300–9600bps) and data format adjustable
quiescent current: 0-30mA
short circuit: 50-70mA with restart function,
line voltage: 30.5V ± 5%, internal resistance overvoltage protection: tranzorb
> 12km@300bps, > 4km@2400bps, > cable JYSTY nx2x0.8
LED indications On, Gsm, Bus, 485
Power supply

Connection: pluggable screw terminal, max 2.5mm2

9-30V DC 10W, reverse polarity and overvoltage protection

230 AC 0.2A, optional, with galvanic isolation



Temperature range

from -20°C to +50°C, humidity <90% non condensing




35mm DIN rail