Re: Positional/physical addressing

Don Y <blockedofcourse@foo.invalid> wrote:

If the controller sends out a pulse and every device responds
instantaneously, the first response received back can trigger a second
pulse from the controller.  The first device on the line will receive
the second pulse after a time which corresponds to twice its distance
from the controller and this can generate a number which the device
stores.  The controller polls through the numbers sequentially from zero
until the first device responds, the controller now tells the first
device to shut up and repeats the entire sequence so that the second
device is now the first one to respond.

 
This is too "high tech".  You're effectively trying to build a TDR into
each device.  Recall, I want these to be dirt cheap because I use so many of
them in a system.

Actually the individual devices just need to store the time between two
clear digital pulses as a number.  If the devices are never closer than
one yard apart, a 300 Mc/s clock speed will be sufficient to distinguish
between them.  (The twin identification pulses will be spaced by double
the path length.)

That programs each device with an unique address and the rest can be
done with normal digital handshaking and read/write.  It is a way of
overcoming the 'identicality' of the devices so you don't have to
allocate individual serial numbers to them during manufacture, which
could reduce the cost if a lot have to be made.

Then they can all be strung out along a two-wire bus (send and return)
to allow individual devices to be removed or changed without a lot of
re-wiring or bridging connectors, so installation and maintenance costs
are reduced too..


--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk