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[hs]

I recently noticed that on occasion, the AHP
software misinterprets change of state
information when other X-10 transeivers are
active.

I happened to have a non-existent lamp
module defined, and was sending data to a
non-existent appliance module (from a simple
X-10 controller) when I noticed that the
lamp module turned off on the AHP screen.

The state of the appliance module was being
used to trigger a macro. The lamp went to
zero and the macro did not trigger.

You can easily re-create this scenario by
adjusting a lamp module brightness and
sending a module off command (at the same
time) from a seperate X-10 transmitter
(simple X-10 keypad/timer console).

I suspect that this holds true during macro-
execution as well.

Is there some type of queuing/buffering
mechanism on the CM15A that is supposed to
prevent such collisions?

BTW - The macros were stored on the
interface, not run from the PC.

Thanks.

[roger1818]

HS:  The CM15a uses X10’s collision
protection algorithm, but not all other
controllers do.  The algorithm works as
follows:

First the transmitter will wait for 8, 9 or
10 (determined randomly) zero half-bits
(each bit is immediately followed by its
compliment (except in the header which uses
1110) in the X10 protocol) on the
powerline.  Then it will start transmitting
data.  If when transmitting a zero it reads
a one, it will abort the transmission and
start waiting again.

This algorithm works extremely well if all
transmitters use it (I will leave it as an
exercise to the reader to figure out
why ).  If a transmitter doesn’t use it,
it could cause a collision.  The CM15a
should recover just fine without losing any
of its own transmissions, but the
transmission from the other controller will
probably be garbled.

[Brian H]

I have seen tests of the cm15a and as Roger
H. said it will wait if a collision is
detected and resend it's data. Things like a
TM751 tranceiver that don't check will have
their transmission trashed.