Re: Positional/physical addressing

Don Y <blockedofcourse@foo.invalid> wrote:

[...]

 My goal
is just to "run wires" between devices and let the devices sort
it all out.

I must admit this problem is a long way outside my comfort zone, but if
we postulate that all the devices are truly identical then the contoller
has no way of initially setting up the system.  If it sends out a
request for a response,  all the devices will respond virtually
simultaneously and there will be no way of sorting out the resulting
'pile-up'

Even if the controller is clever enough to detect the nearest device on
the line, because its response arrives first, it has no way of telling
that device to assume a particular identity because the same identity
command will be picked up by all the other devices too.  The problem
isn't one of which system to use, but whether an overall strategy can be
developed to solve a problem that appears to be logically insoluble.

Having said that, there is one feature that could be used to distinguish
between the devices before any address allocation has taken place, they
are all different distances from the controller. 

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 repeated until each device along the line has a unique number
and has been muted..  The controller sends out a command to re-activate
all the devices and polls through the numbers again, listening for each
device to respond individually.  When a device responds it is allocated
a proper address and the network is gradually set up in this manner.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk