davidt Posted August 27, 2003 Report Posted August 27, 2003 I need the documentation of the modbus-protocol in order to write a driver between the pc and the plc. with best regards. Quote
Jay Anthony Posted August 27, 2003 Report Posted August 27, 2003 I have been collecting Modbus documents for about five years as I also had to write a Modbus driver. The standard obviously is dictated by the originally company Modicon (now a part of Groupe Scheinder.) Please understand that as a defacto standard for communications in the process and instrumentation industry, the protocol has been amended (and corrupted) for other manufacturer's uses. Please check carefully as the many methods of representing double length words and floating point numbers are vast. The most accepted version of this is the Daniels-Enron extension to the Modbus protocol of which there is no electronic docuimentation that I can find. If your project needs either double word or floating point numbers, I have several documents which would lend some insight into this extension to the Modbus protocol. The official organization that governs the Modbus protocol is Modbus.org Modbus.org Another good site for research is the Modbus community: Modbus Community sponsered by control.com Check also this thread on this forum: Floating Point Registers at MrPLC.com ModBus_Standard_1996.zip Quote
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