I am trying to read 32bit modbus registers with a Siemens S7-200 PLC and a Delta motion controller. I can do this just fine, except that I must read the 32bit register as two 16bit registers. The problem is that the two 16bit registers are read backwards. AKA if you look at the hex values...

Source:12345678
Read from Source:56781234

How do I read them in the correct order? The Siemens library only lets me read words or bits. I have thought of a couple ways to do this but I really don't want to have to write a communications buffer for every command I send and receive as there are about 15 separate 32bit values I must send and receive every cycle...

 

There may be a software solution for you, I do not know. I do know that you could use our hardware to reverse the words for you with no additional programming on your part. Please have a look at our Omnii-Comm
http://www.miille.com/din266-p00.pdf for more information.

Jerry Miille

 

Is there a version of ModBus that is geared to 32 bit registers etc?
Someone was implying there is a 32 bit variant(?)

 

If there could be variations to the original modbus protocol I ensure you that someone has made it. Our Modbus drivers, in KEPserverEX, have 2 pages of configuration settings to take them all into account.

You can try it out in the full functioning demo at http://www.kepware.com.

Fred Loveless
Kepware Technologies

 

Hi guys,

The Modbus version with 32 bit registers is also known as Daniels Modbus or Enron Modbus.
I know that flowmeters, with modbus, usually have this type of Modbus since they need to present float values. Some of the flowmeters also have 64 bit registers, also in order to present float.
Many Modbus RTU masters have problems reading 32/64 bit registers.

HMS have a gateway, that can poll any type of register and put the values into normal 16 bit registers, for more info go to:
http://www.anybus.com/support/support.asp?PID=317&ProductType=Anybus Communicator

or send me an email at: [email protected]

//Patrick L