Hello folks, I wanted to implement Modbus protocol on fpga. I don't know how to start? I read various documents on internet but didn't got any clear idea. basically my aim is to make package of this protocol. I am using Vhdl as la nguage. so i want process or say steps should i follow to make this protoco l working.If anybody has worked on this previously can share document it wi ll be great help. thanks in advance..!!
There are basically two ways to do Modbus. One is Modbus RTU, using a UART with RS-485. On the hardware side you need a UART with a transmit enable control line. Everything else is in software.
The other is Modbus TCP/IP over Ethernet. On the hardware side, you need Ethernet. Everything else is in software.
So "Modbus on an FPGA" means having a processor (soft or hard) and software on the FPGA or the board, and a UART or Ethernet. Trying to implement Modbus directly in FPGA hardware without a processor is insanity.
Thanks David for information. I just wanted to know that are you suggesting to use external processor for implementation.
and also i would like to know while writing vhdl program what steps should i follow.
I am suggesting you use a processor for handling the protocol. It is entirely up to you if this is external to the FPGA, a hard core in the FPGA, or a soft core in the FPGA.
If you have to ask this, I would recommend that you drop the idea of an FPGA altogether. A $2 microcontroller will let you build a Modbus RTU slave on RS-485 - it will have a UART and all the processing power you need. If you are thinking of Modbus over Ethernet, your microcontroller will be around $5.
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