Modbus/TCP has been around a while - yet most people
have neither heard of it nor have they been introduced to the absolute simplicity
and brilliance of its use for multi-vendor TCP/IP networks. True,
it is used to talk to Modicon PLC with Ethernet adapters, but it is not an exotic,
complex new protocol like other developing standards - merely Modbus/RTU in a
TCP/IP wrapper! So the real beauty of Modbus/TCP is in how fast it can be
implemented and how easily the data is to integrate into existing applications. 
Any company with the following three (3) resources can implement Modbus/TCP
in a few days:
- Source code for an existing Modbus/RTU serial driver
- TCP
socket library for their hardware
- A competent programmer
So presto,
vendors can have a Modbus/TCP driver almost instantly. Any application program
which supports the data access paradigm of Modbus/RTU also supports Modbus/TCP
instantly with this new driver. Direct Modbus/TCP access by Ethernet can
also offer good performance - ModiconÕs documentation shows that up to 5000
or more registers may be transferred per second. Try that with Modbus/RTU
on RS-232 at 9600 baud! Of course, if your access is through a Modbus/RTU
to Modbus/TCP gateway, you will STILL be limited by the performance of the Modbus/RTU
serial line.
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