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Andy Neil
04/26/04 09:53
Read: 849 times

#69216 - Its not difficult...
Responding to: Joseph Hebert's previous message
Joseph Hebert said:
I've never figured out that whole ninth bit multiprocessor mode thing either.

If you have ever used an automatic vending machine, the chances are that the transaction relied upon it!
So don't dismiss it!

All messages from the master are sent to all Slaves.

The slaves examine the address in the message, and respond iff the address matches the particular slave's address.
Address bytes are identified by setting the 9th bit.
(this can all be handled in hardware with the Enhanced seial interface).

In vending machines, the Master also polls the slaves peiodically - so that the slaves can send messages to the master other than in response to a command.

Obviously, you need a suitable bus architecture to allow all of the slaves to be connected to the master's single receive line - so you can't do it with RS232.

But just because you can't do it with RS232 does not mean to say that there aren't other ways!

If all the slaves are on the same PCB, simple open-collector drivers and a pullup resistor will do.

In vending machines, an opto-isolated current loop is used

List of 9 messages in thread
multiprocessor communication      M.Jawed Iqbal      04/24/04 17:20      
   RE: multiprocessor communication      Joseph Hebert      04/24/04 18:21      
      Its not difficult...      Andy Neil      04/26/04 09:53      
   RE: multiprocessor communication      Kai Klaas      04/24/04 19:38      
      new testament      Andy Neil      04/26/04 09:41      
   RE: multiprocessor communication      Erik Malund      04/26/04 07:28      
      new testament      Andy Neil      04/26/04 09:38      
         RE: new testament      M.Jawed Iqbal      04/28/04 18:04      
   RE: multiprocessor communication      Ashish Pradhan      04/26/04 11:34      

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