[TECH]From Engine to Caboose, What's in the train?
Dennis Plunkett email (remove spam text)
At 11:09 12/10/99 -0400, you wrote:
Time for my input!
Ok all seem to go along the same lines.
But (Always a but)
None of the systems are fault proof
None of the systems indicate full sting connection
To do this imagine:-
Engine (Does not matter if there is more than one, but this is the master
End of train (Not all tranis have a cabose!)
The end of train marker will provide the loop back point (This will also
alow the system to verify that the train is intack (A problem faces when
passing loops are used Ask Annie!)) This will loop the data directly back
to the master
The master end starts sending out NULL byte
Each other item in the link will pass the Null bytes on
The master then counts the number of bytes that it takes to get the NULLs
back i.e. The system is a full loop and the master will then KNOW how many
carriges, and the expected train length.
The mater then sends out the start of message byte.
Each carrige will see this and know that it has to send out its own address
(Value). The second byte from the maste will have the number of expected
carriges, and the third byte has the current carrige number.
The current carrig number is incremented by the current carrige and points
to where in the stream it will place its address. All carriges will inspect
the current carrig number and the expected number, if the current is
greater it will hold the data line low (Clock NULLS to indicate an error)
There are many other things that you can add to this to improve the
reliability. You must remember that this is to be a failsafe system, and
should report an error if it is not working, no assumptions can be made!
See also: www.piclist.com/techref/index.htm?key=
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