The Industrial Raspberry Pi Forum

We are configuring PiCtory in RevPi Connect to communicate with MODBUS RTU Slave device and have a question below.

1) We need to send below message -> How to set the Extended Data in PiCtory correctly?
01 03 00 00 00 04 44 09

Please refer to the attached figure for the command and return.

It is confusing with the term "Quantity of Registers" in PiCtory since changing from 1 to other value has no different.

While the only option is to read from adjacent Register Address and then perform some calculation on your own, with this, maximum Quantity of Registers that RevPi can read from Modbus RTU Slave is only 2.

Then it is impossible to read anything from your Modbus Slave that need Quantity of Registers more than 2 at all.

In this case the sensor needs to be read at 4 registers together so RevPi doesn't actually work with all type of Modbus RTU.

Is this some kind of limitation of the RevPi itself?

Please help correct us if we were wrong.

From the Modbus RTU frame format in previous post,
03: The function code (read analog output holding registers)

0000 The data address of the first register requested
0004 he total number of registers requested. (read 3 registers 40000 to 40003)

https://revolution.kunbus.com/tutorials ... -turorial/

http://www.ozeki.hu/p_5854-ozeki-modbus-rtu.html

Pictory Modbus action configuration for the query would be on following basis:

Thank you Amar, that is exactly correct and make it worked!

One important thing is that when the QTY is not 1 then the rest will be automatically allocated to the next available variable name.

Taking below quote from this tutorial - https://revolution.kunbus.com/tutorials ... -turorial/

Example: 4 bytes from “Output_1” also occupy “Output_2″,”Output_3” and “Output_4”. To avoid overlapping, in this example you have to set the next command to “Output_5”.

Nice. That's right. QTY to read multiple registers (more than one) will automatically allocate to the next available variable name. Your Example to avoid overlapping is also correct.