Need Information about Implementing of Modbus protocol in fpga ( mostly spartan 6)

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 language. so i want process or say steps should i follow to make this protocol working.If anybody has worked on this previously can share document it will be great help.
 thanks in advance..!!

On 26/11/18 11:08, Swapnil Patil wrote:
> 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 language. so i want process or say steps should i
> follow to make this protocol working.If anybody has worked on this
> previously can share document it will 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.

On Monday, November 26, 2018 at 3:42:10 PM UTC+5:30, David Brown wrote:
> On 26/11/18 11:08, Swapnil Patil wrote:
> > 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 language. so i want process or say steps should i
> > follow to make this protocol working.If anybody has worked on this
> > previously can share document it will 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. 

On 26/11/18 13:09, Swapnil Patil wrote:
> On Monday, November 26, 2018 at 3:42:10 PM UTC+5:30, David Brown
> wrote:
>> On 26/11/18 11:08, Swapnil Patil wrote:
>>> 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 language. so i want process or say steps
>>> should i follow to make this protocol working.If anybody has
>>> worked on this previously can share document it will 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.

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.

> 
> and also i would like to know while writing vhdl program what steps
> should i follow.
> 

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.