Can I…/ What can I do…?

I have a problem by reading the value of the Temperature and Humidity Sensor attached to a RevPi Core by using RTU Modbus Master and USB RS485 Slave. What can I do?

Please follow the link below: Rtu master to temperature sensor rs485-usb - Revolution Pi Forum

I use the Virtual Modbus Master in PiCtory and have communication problems. What can I do?

There was a problem in the pimodbus-master daemon, which we fixed in the current Debian Buster, see Forum

https://revolutionpi.de/forum/viewtopic.php?f=6&t=2939&start=10#p10950

However, there is another item on our to-do list here, which is that the PiCtory project file is not backwards compatible.

A workaround is to recreate the PiCtory project on Buster.

I have questions on the node-red-contrib-modbus what can I do?

Node-RED and the RevPi Nodes for Node-RED are third party products. Please ask for help in the Revolution Pi Forum here: https://revolution.kunbus.de/forum/viewforum.php?f=48

I want to change parameters of the Modbus Master communication, but I can't find them in PiCtory. For example Timeout or Inter-Frame Spacing Timer. What can I do?

• These parameters are included in the "libmodbus" library. You are welcome to modify them yourself.

• https://revolution.kunbus.de/forum/viewtopic.php?f=6&t=2023&hilit=modbus+timeout&start=20

How to …?

How to configure a (Virtual) Modbus TCP Master in the Revolution Pi

Have a look in the link below:

Is there …?

Is there a practical example of putting a Modbus client into operation?

Take a look at this wonderful troubleshooting as an example of how it works:

Is there an industrial switch I can use with a Revolution Pi module?

Take a look here:

Is it possible to write only once, instead of continuously using the Modbus TCP Master?

It is not possible to write only once with piModbusMaster.
For this, you can directly access the libmodbus API from another application on startup for making needed initialization and thereafter start piModbusMaster service.

LibModbus

Others Questions…?

How many Modbus-RTU Servers (slaves) are addressable?

• The maximum addressable Modbus-RTU Servers are 247

• But per RS485 segment, there may be a limitation to 32 devices on a serial line because of the serial driver

• Original discussion