I was hoping someone would be able to help me interpret what I believe to be is extended modbus. I am trying to map to a modbus controller from the DCS and I am having issues with the addressing. There is an address 428893, which does not fall within the typical modbus that I am accustomed to. I spoke with a representative for the company and they told me to drop the first 4 in the address but this would leave me 28893 which again does not fit into what I know for typical modbus addressing. If someone could please tell me how I would map this, it would be greatly appreciated.

Thanks in advance.

 

Hello,
4 means the Holding Register
28893 means the HR address (it can be 1-65535).

Regards,
Andrzej
www.modbus.pl

 

Thank you for your reply. I think I will need to flash my serial card with an extended modbus driver. It typically will put in the 4XXXX when I assign it to be a holding register, which is where I was getting confused.

Thanks again for your help.

 

The term "extended modbus" is new to me. Never heard of it during 19 years with Modicon/Schneider. The data type is 0, 1, 3 or 4. This is part of the message header. The address therefore can have 16 bits all to itself. 0 to 65535. Any address is valid if it is supported in the end device. You cannot read 27534 if the registers in the device end at 20000. I just did an application where the modbus addresses of the holding registers were in the 64000 area. Also, some devices have been known to set address areas as unreadable as they are only used internally.

 

The question is about 5 bit (4xxxx) or 6 bit (4xxxxx) addressing.

One earlier thread (Aug 27, 2002) discussed it:
http://www.control.com/thread/1026155725

I guess an open protocol leads to 'open' terminology for discussion purposes.

 

The Original Poster may refrain from calling a 5-Digit Modbus Address as "EXTENDED MODBUS".

The Modbus Address Format mentioned by the Original Poster is simply a "Standrad Modbus Address Format".

Standard Modbus Address Format comes with a prefix of 0, 1, 3 or 4. + UP TO 5-DIGIT-LONG resolution, depending on the type data is should represent.

The length of the address may depend on the capability of the Modbus equipment, and it may also depend on the way it was mapped in a Modbus Device by choice of the programmer/OEM.

"EXTENDED MODBUS" is different.