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The information on this web page is either Lynn's opinion or something Lynn agrees with. He has complete control over its contents. Nothing contained within this pages is approved by or represents the opinion of Digi International, The Modbus Organization, the Modbus-IDA Group, ODVA, or any other organization Lynn is associated with.

Use of XML

My main interest in XML is for configuration. I see some value in 'public data exchange', but existing binary protocols will remain the bulk of data exchange. I also hope to start defining some simple "encapsulation" schemes for remotely routing things like Modbus through HTTP. But this page is not a priority for me right now.

Will XML use be common in PLCs? (warning: Lynn's opinion)

Don't expect XML in most PLC - the information content to too low per byte. This means it takes 100 or even 1000 times MORE bytes to say the same thing as a binary protocol like Modbus or Ethernet/IP. Plus XML forces the PLC to convert binary values (ints, floats, etc) to/from ASCII strings - to things like 000023.45677. This is very inefficent and you'd end up needing to add an extra high-end CPU just to handle the added overhead of all this ASCII string conversion. This means the field device would need a list price $50-250 higher than a model without XML.

Yes, a niche market will evolve with XML at the end device. But a vast majority of users will stick to faster binary protocols in the field and do any XML work they need at the enterprise level (ie: server to server or with outside partners) and not at the controller level.

Plus XML isn't magic - you'll still need to know how to map a tag like to another vendors . XML is just a format, not a "protocol". It won't make comms free & easy - you still need to pay XML experts to customize things. But you CAN customize things - that's why the enterprise people are so happy. No magic, but it can be MADE to work somehow. That's the XML value.