>Hi PICers,
>
>I thought that a HUB is something that would be able to work only with
>devices that share the same kind of hardware and software protocol. In the
>case of a general RS232 HUB, each device would be working in a different
>boud rate and would most probably have a different software protocol. How
>can such HUB overcome such a problem ?
>
>Chaipi

One possibility is to use an RS485 network and hang a series of pic-based
modules on each node. Use two spare conductors to power the modules and you
have a single cable which goes to everything in the lab.

The numbered slave modules receive at 110 kbaud and buffer the message, then
transmit it to the equipment in an appropriate way. They then buffer several
bytes of response to upload. This way the modules can be configured for a
variety of protocols, and even GPIB though this is more difficult.

The master has to do a bit more work. If only a single slave is needed at
one time there is no problem. It just breaks the serial data stream into
packets and sends them out when the slave node is ready for them. The slave
responds by sending back the contents of its buffer.

If several nodes need to be used (DVM, voltage supply, and signal generator
for example) then the master may have to buffer data from several sources
and feed them to the host. This is much more complex and some sort of
polling would need to be implemented.

I'm sure there are several other solutions to this problem, but I'm looking
at RS485 for another similar problem. Hence my suggestion.

Keith.
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Keith Dowsett         "Variables won't; constants aren't."

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