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Forum Index : Microcontroller and PC projects : Modbus docs no longer a free download

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PhenixRising
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Joined: 07/11/2023
Location: United Kingdom
Posts: 1581
Posted: 02:16pm 21 Oct 2025
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  Quote  I went to find the download link to reply to someone inquiring about Modbus RTU CRC and was quite surprised that Modbus.org has removed its published specifications/standards from their formerly open, freely accessed web page.

I thought maybe it was just a simple registration to get access, but the attempt to register on the Modbus.org site brought up the need for a billing address, so registration is clearly now a paid registration. I poked around to discover that Modbus.org has several different levels of membership, but cost of any membership level is not disclosed up front.

The term "open protocol" has been new-speaked in the past couple decades to mean "available for a price", as opposed to the former Modbus truly open, download-the-spec open. That's the path that Modbus's owners have chosen.

In 20 odd years of hanging around control.com, I have never been a fan of just pointing users who are attempting to implement Modbus to the spec/standard because implementing Modbus in the field is typically a case of using commercial devices and software that one presumes have some relatively high degree of functionality. The specs/standards are more aimed at a coder looking to code Modbus. And it worked to provide a link to the standards.

Admittedly, there are sites other than Modbus.org that have posted the various Modbus specs.

So I wonder, will the absence of formerly, freely accessed specs coupled with some (unknown) cost for Modbus membership limit the future implementation of Modbus?


And then...

  Quote  Btw, edu membership is 500USD


MB-TCP-Security-v21_2018-07-24.pdf
ModBus Conformance Test Spec_v3.0.pdf
Modbus_Application_Protocol_V1_1b.pdf
Modbus_Messaging_Implementation_Guide_V1_0b 2006.pdf
Modbus_over_serial_line_V1_02.pdf
 
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