Hi all

I'm still "listening" but need more time for coding. I played some with the Opto Enet rack today and got more serious about Modbus/TCP. It seems the Opto "Brain" (isn't that corny) "supports" Modbus/TCP, but does it in an interesting fashion. Reading digital inputs you get 1 input per address as a 16 bit "register". I was expecting some way to pack several inputs into a register for efficiency. It seems you get 0 or 255, not 256 like if you had the bytes swapped? more on this later. I'm gonna write a packed dumper so I can see what's really going on.
They also talk to it in an IEEE1394 "firewire" packet format over TCP. Since this supports "quadlets" and bitmaps I would guess it's more efficient. I wonder if they didn't cripple the Modbus just a little to steer you to their proto. Has anyone seen anything else that uses the IEEE1394 block format? Would it be worth implimenting?


Curt Wuollet,
Wide Open Technologies

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On Mon Jan 10 17:47:02 2000 Curt Wuollet wrote...
>
>Hi all
>
>I'm still "listening" but need more time for coding. I played some with the Opto
>Enet rack today and got more serious about Modbus/TCP. It seems the Opto "Brain"
>(isn't that corny) "supports" Modbus/TCP, but does it in an interesting fashion.
>Reading digital inputs you get 1 input per address as a 16 bit "register". I was
>expecting some way to pack several inputs into a register for efficiency. It
>seems you get 0 or 255, not 256 like if you had the bytes swapped? more on this
>later. I'm gonna write a packed dumper so I can see what's really going on.
>They also talk to it in an IEEE1394 "firewire" packet format over TCP.
>Since this supports "quadlets" and bitmaps I would guess it's more efficient.
>I wonder if they didn't cripple the Modbus just a little to steer you to
>their proto. Has anyone seen anything else that uses the IEEE1394 block format?
>Would it be worth implementing?

Embeding a single digital value inot a whole register is not at all
uncommon in the third party ModBus bussiness. I can't speak for
Modicon, having never used an actual ModiCon PLC. I have however used
the ModBus protocol to talk to many third party products.

--
Stan Brown [email protected] 843-745-3154
Westvaco
Charleston SC.
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