Could I have some opinions please. This sounds complicated
at first glance but I'm sure there's a chip that'll help me out

I've a job to look at that requires several, possibly a dozen,
modules to hang off a PC com port. The PC holds 20-byte
packets, which are complete messages in themselves. It
has to look for a module that's not busy and send it a packet.
The PIC in the module performs a small calculation and then
returns the result back to the PC. BUT before it returns the result
it has to wait maybe several seconds before doing so. This
is because another external device has to do something the
module will refer to. This means I can't perform the whole
operation in sequence with each module before moving on to
the next.

In other words, 10 packets may be thrown out to 10 modules but
each module will take an indeterminate time to return the result
to the PC. A new packet might be available to send to this free
module immediately, but if there isn't then this module will have
to be ear-marked as free for the next available packet

Each module can be assigned an ID number as part of the
packet so the PC will recognise where a returned result came
from. All of the modules will be together physically as plug-ins
on a motherboard, which has one short cable to the PC

1:1 comms between a PIC and a PC I can manage, but what
would be the most efficient way of fanning out a PC port to
several devices ? I'm looking at either 19k or even 56k but
speed isn't critical, particularly with such small finite packets.
What I'd like to know is more about how to create a system
that can be polled for an available module. Modules may be
added or removed so the system has to be somewhat flexible.
There can be no inter-connectivity between modules. Cost is
especially critical - I'm stumping up for the prototype !!! But
it's a shared venture and I daresay I'll be re-imbursed one day

Which protocol would be most suitable ?

What glue could I use between the PICs and the PC to indicate
that a module is busy and/or is ready to send its result ?

Is there a way to poll, for example, a Busy pin or would the PC
have to re-communicate with each module to find out if it's still
busy or free for a new packet

TIA
__________________________________________
Even if you're on the right track, you'll get run over if you
just sit there

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