M-Bus Master Click Board™

How Does The M-Bus Master Click Board™ Work?

The remote reading of heat meters can take place in different ways. Besides the remote reading, the whole collection of various meters can be remotely controlled over M-Bus, making it a complete housing solution. The latter is a logical continuation/extension of the technical development of consumption meters and is realizable with the help of the M-Bus Master Click Board™.

In order to realize an extensive bus network with low cost for the transmission medium, a two-wire cable was used together with serial data transfer. In order to allow remote powering of the slaves, the bits on the bus are represented as follows:

• The transfer of bits from master to slave is accomplished by means of voltage level shifts. A logical "1" (Mark) corresponds to a nominal voltage of +36 V at the output of the bus driver (repeater), which is a part of the master; when a logical "0" (Space) is sent, the repeater reduces the bus voltage by 12 V to a nominal +24 V at its output.
• Bits sent in the direction from slave to master are coded by modulating the current consumption of the slave. A logical "1" is represented by a constant (versus voltage, temperature and time) current of up to 1.5 mA, and a logical "0" (Space) by an increased current drain requirement by the slave of additional 11-20 mA. The mark state current can be used to power the interface and possibly the meter or sensor itself.

As mentioned above, M-Bus standard has predefined voltage levels and principle of work. In order to achieve that, the M-Bus Master Click board™ has built in complete solution for master node on the network, based on MC33072ADR2G – monolithic, single supply 3 - 44 V operational amplifier from ON Semiconductor. Besides the operational amplifier, this click board has all other needed components needed to achieve a complete analog solution which, on its output, fulfils the M-Bus voltage and current predefined specifications.

The M-Bus Master Click board™ also has VOM452 onboard – the analog, high speed, high noise immunity, 1 MBd optocoupler, from Vishay Semiconductors. These high speed optocouplers, each consists of a GaAlAs infrared emitting diode, optically coupled with an integrated photo detector and a high speed transistor. The photo detector is junction isolated from the transistor to reduce miller capacitance effects. The open collector output function allows circuit designers to adjust the load conditions when interfacing with different logic systems such as TTL, CMOS, etc. All these features improve the reliability of the whole circuit, while enabling the galvanic isolation.

The M-Bus Master Click board™ offers a selection between 3.3V and 5V operation, with the onboard SMD jumper, labeled as PWR SEL. This allows both 3.3V and 5V MCUs to be interfaced with this Click board™.

SPECIFICATIONS

PINOUT DIAGRAM

This table shows how the pinout on the M-Bus Master click corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

ONBOARD SETTINGS AND INDICATORS