managing the modbus sniffer configuration file

THEMIS/BIOS is using PROMUX modbus modules :

• PM6RTD for PT100,
• PM8TC for thermocouples
• PM16DI to collect digital boolean signals (high/low, open/closed, on/off)

To autodiscover which devices are on a bus, a tool is available.

cd /opt/openenergymonitor/BIOS/hardware
python3 promuxDiscovery.py

The modbus.conf file is structured in 3 sections : common, bus and slaves

common section

The common section gathers the connexion parameters :

"common": {
    "modbus_IP": "192.168.2.1",
    "tcp_port": 503,
    "baudrate": 9600
}

slaves section

For most common situations, a minimalistic configuration is possible :

"slaves": {
    "PM6RTD": {
        "id": 0,
        "promux": 1,
        "mode": "input"
    },
    "PM8TC": {
        "id": 1,
        "promux": 4,
        "mode": "input"
    },
    "PM16DI": {
        "id":2,
        "promux": 1,
        "register": 0,
        "mode": "discrete"
    }
}

It is possible to have 2 equipments of the same model on the bus, as long as you take care to give them each a unique modbus identifier. It is enough to use different names: PM6RTD-1 and PM6RTD-2 for example, but the model MUST appear in the hardware name.

You can add a register key to specify at which address to start reading.

Default value for the register key is 1 :

• when reading input registers, like PM6RTD or PM8TC, with an offset of 30001, reading will start at register 30002.
• when reading discrete registers with a PM6DI, with "register": 0, reading will start at address 10001

The promux key permits to autoconfigure the target module.

A more complex configuration can be achieved in order to describe for each unitid on the bus :

• which registers to read
• how to format payloads for the MQTT broker

To refine the configuration of a module/node, you can add :

• a unique datacode (“datacode” key) or an array of datacodes (“datacodes” key) with as many elements as we have registers to read
• an array of names to be used in the MQTT publication process (“names” key)
• a multiplier coefficient (“scale” key) or an array of multiplier coefficients (“scales” key)

Please note :

• the default datacode is h, ie 16 bits signed integer
• the default multiplier coefficient is 1

Below is transcripted what could be a complete configuration for a PM8TC :

"PM8TC": {
    "id":1,
    "promux": 4,
    "registers": [0,1,2],
    "names": ["serial","TC_1","TC_2"],
    "datacode":"h",
    "scales":[1,0.1,0.1]}
}

bus section

The bus section is a table listing the names of the equipments in activity on the bus.

bus = [ "PM6RTD", "PM8TC" ]

With such a bus section, the modbus service will only retrieve datas coming from the (PM6RTD, id=0) and from the (PM8TC, id=1).