Modbus ASCII on the Anybus Communicator

Anybus Support Anybus Gateways
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#1

Hello,

We have a customer that needs to use the Anybus Communicator to get data from a device that only supports Modbus ASCII. I found reference to Modbus ASCII in the User Manual. (HMSI-27-316, Rev 1.00, page 80)

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However, I have not found any specific documentation on how to set up Modbus ASCII Commands or Transactions in the Anybus Configuration Manager. Should the Commands be set up the same as Modbus-RTU? The Checksum has an option to be configured for ASCII, but I don’t see a means to do it for other parts of the command. Please let me know if there are any reference materials to help me understand this.

Thanks!
Trevor

#2

Hello,

We do not have any reference material or examples on setting this up. Modbus ASCII is basically Modbus RTU except every character of the Modbus RTU Request and response is broken out into the characters ASCII code. This doubles the amount of data and effort necessary.

From the diagram I may have a better and significantly easier solution. Our transparent Modbus gateway, the AB7702, supports conversion from Modbus TCP to Modbus ASCII. Since the communication through the gateway is transparent it takes no effort for configuration. More information can be found here,

https://www.anybus.com/support/file-doc-downloads/gateway-specific/?orderCode=ab7702

#3

Hi Nick,

Just so that I get this correct:

  1. Connect the Modbus ASCII devices (three) to one AB7702 gateway to convert to Modbus TCP.
  2. Connect Gateway to the site’s Ethernet network.
  3. Read devices from gateway either through PLC (Rockwell) or SCADA (Inductive Ignition).

Thanks

#4

If you are using an Allen Bradley PLC this would actually not work, as Allen Bradley PLCs use Ethernet/IP not Modbus TCP. Perhaps the SCADA uses Modbus TCP?

If you must use Ethernet/IP then the AB7072 (or AB7007) would need to be used. However, as indicated before it would take some effort to implement the Modbus ASCII protocol in the Anybus configuration manager software.

#5

We’ll be using the SCADA system and it does support the Modbus TCP.

#6

To be clear the SCADA is a Modbus TCP client/master? If so, the AB7702 would likely be a better solution for this application.

Best regards,
Nick

#7

Nick,

Yes, Ignition has a Modbus module which is a master only.

Thanks

#8

Great, I do think that AB7702 is a better option.

Thanks!

Nick

#9

Thank you Nick. So, I’m thinking I’ll get one Modbus Gateway (AB7702) and connect three devices as a slave. Should be straight forward…

#10

That sounds correct to me, thanks!