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Converting the Modbus ASCII to Modbus RTU
Is there a converter that can convert the Modbus ASCII protocol to the Modbus RTU?
By Huang Jinsong on 13 January, 2004 - 2:14 pm

Dear Sir,

Is there a converter that can convert the Modbus ASCII protocol to the Modbus RTU? for our controller only support the Modbus ASCII, and the Master only support the Modbus RTU. How to set up the communication between these two devices?

Thanks and Best Regards
Huang Jin Song

By Richard Theron - FieldServer on 13 January, 2004 - 5:04 pm

Hi Huang

FieldServer Technologies has a protocol converter that will map Modbus RTU registers to Modbus ASCII, for further information please have a look at The FieldServer is configured by mapping the data points from one protocol to another.


By Jerry Miille on 13 January, 2004 - 11:19 pm

The MARC Multii-Port module can translate between the two protocols. See this link for additional information or contact me directly at

Jerry L. Miille

The Modicon BM 85 bridge mux will perform Modbus RTU to ASCII or ASCII to RTU conversion.

By Lynn at Alist on 15 January, 2004 - 6:58 pm

This may be overkill - but virtually ALL of the Modbus/TCP-to-Serial bridge products can handle either MB/RTU or MB/ASCII. This includes the Modicon CEV and our DigiOneIA-RealPort. So a pair of them can map Modbus/RTU to ASCII, plus open up "multi-master" access.

So if your controller polls through such a bridge, it would map Modbus/RTU to Modbus/TCP. Then the 2nd bridge would map Modbus/TCP to Modbus/ASCII. So your MB/RTU master can poll your MB/ASCII controller.

As a "free" side benefit, you can now use your notebook computer (or an HMI) to access your MB/ASCII controller with Modbus/TCP AT THE SAME TIME! This is the "multi-master" benefit of using Ethernet bridges - the
bridge acts as a proxy master to your controller.

best regards
- LynnL, Snr Prin Engineer
for email address see:

By Curt Wuollet on 16 January, 2004 - 12:00 pm

My favorite way would be to write code to do the conversions as a filter and pipe a pair of them between the application and the serial port.




I'm interested in this topic. Is there any reference material that i can follow to write the code??



Equustek makes the DL4000-MMX.
It is a Modbus RTU slave and then translates it to Modbus ASCII Master.
So your Modbus RTU master SCADA other device can communicate with Modbus ASCII slave devices.