At 11:58 PM 6/26/2003 +1000, you wrote:
>I have been asked to install and commission a cryogenic temperature
>controller. The system uses a mixture of various commercial components
>to provide closed loop temperature ramping from -200C to +10. Several of
>the components provide control via a MODBUS interface. We wish to make
>use of this feature but we have no experience in programming the MODBUS
>protocol. The physical interface is half duplex RS485, 9600 baud, 8E1.
>
>Can any one guide us to some sample code, in either VB, VC++ or Delphi
>which we could use as a starting point. I have scoured the Web but have
>found no really good examples. The control system will operate,
>ultimately, from a Linux system, so ANSI C examples would be preferred.
>
>Thanks in advance.


There's some links on my web page, some of them may even still work.

There's 3 basic types- Modbus (ASCII, serial) and Modbus RTU.

The issue with Modbus RTU (which is more efficient) is the tight timing
that is required for framing.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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