Extended MODBUS Addressing 1

[catserveng]

I have an AB SLC5/04 with a Prosoft MVI46-MCM installed, I am trying to get data from two Woodward EasyGen controllers. The EasyGen's use extended MODBUS addressing, haven't been able to find how to use extended MODBUS addressing with the SLC and the MVI module.

When I use Modscan32 I use an address of 50001 and can recieve the desired data. If I try a number larger than 32767 in the config file for the MVI module in the SLC I get an error.

Any ideas? I'm in a gas field in Texas and I am running out of ideas.

Thank you, Mike

 

[catserveng]

Sorry, should have added the address I'm trying to use is 450001.

Thanks,

 

[danw2]

I have a situation coming up that is similar, extended addressing in the 4xxxxx range.

The MCI46-MCM manual (pg 69) says:
5.8.3 Read Holding Registers (Function Code 03)
Query
Read holding registers (03) allows the user to obtain the binary contents of holding registers 4xxxx in the addressed slave.

which is the legacy address range, even though Modbus register addressing can go up to FF FF (65535 decimal)

I tried Prosoft's knowledge base and it only produces a query referencing an interpretation of addressing which results in a negative address value to the valid range of 4xxxx, inferring that values above 32xxx are interpreted as negative values (makes sense, MSB is sign bit).

I also tried Prosoft's forum, but it failed 3 times to accept my post, blaming my 'code'. A typed text question with background explanation is code?

Catserveng, if you find an answer, please post it here.

Dan

 

[catserveng]

Got this today from ProSoft, it worked.

The MCM will work with the extended addressing. Depending on how the Woodward works you may need to enter the offset of 5000 in the Dev Addr field in your Modbus command, or possibly 50000.

If it's 50000, since Rockwell uses signed integers, we'll need to subtract 65536 which means the Dev Addr in your MCM command will be -15536. The value may look strange, but it's the same bit pattern as 50000 unsigned. Don't hesitate to send us a reference to the Woodward unit if you have any problems with the Modbus commands.


Best regards,

Steve Crippen
Prosoft Technical Support

 

[danw2]

Thanks, Steve.

Dan