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Path: utzoo!attcan!uunet!snorkelwacker!ai-lab!melnik@gnu.ai.mit.edu
From: melnik@gnu.ai.mit.edu (Ofer Melnik)
Newsgroups: comp.protocols.misc,comp.protocols.iso
Subject: which protocols to use ??
Message-ID: <11347@life.ai.mit.edu>
Date: 13 Oct 90 07:01:30 GMT
Sender: news@ai.mit.edu
Organization: MIT Laboratory for Computer Science
Lines: 36


 
HI,
 
A group of friends and I are in the process of creating an intelligent
data acquisition system; We are currently in the specifications phase of
the communications protocol and we seems to have run into an impass.
 
This is a rundown of the system; It consists of one master (an MSDOS machine)
and up to 256 slave terminals. The physical form of communications employed
between the machines is analgous to radio-communications over a single
frequency. Meaning there is one common half-duplex channel which everyone
listens to. The flow of communications is basiclly polling; The master
repeatedly polls each slave, either receiving data from it or reprogramming
it. Broadcast communications are also possible (master initialization
of all slaves).
 
As we see it asynchronous communications is the only
viable form of communications possible over this one-line for 2 reasons.
The first being obviously that we have no way to send a clock over the
line. The second is that synchronous communications without additional
hardware is usually CPU expensive (constant processing of received
information). If it werent for this asynchronus need we would have
used simple SLDC.
 
We would like to be able to implement the protocols using minimal
hardware. Meaning the only addition to the PC would be a form of modem
connected to the serial line. And on the terminas we would like to use
the serial line already existant on a 8751 (8051 microcontroller + EPROM).
And if the protocol is purchaseable all the better.
 
What protocols would you recomend for our applications?? Any infrmation
would be greatly appreciated.
 
Thanks in advance.
Ofer MElnik