Re: XTB-II TW523 Emulation

[nobody@xxxxxxxxxxxx (Dave Houston)]

"Jeff Volp" <JeffVolp@xxxxxxx> wrote:

>The one thing I am concerned about is collision detection.  Documentation
>for the TW523 says: "Any signals applied to the O.E.M. product are
>error-checked, valid X10 codes."  Since all bit patterns are defined, the
>only possible errors are a bad start pattern, or a mismatch in the bit
>halves.  The XTB-II rejects any message with either of those errors.  During
>transmission, X10 says: " The ability to read X-10 codes from its own output
>also allows the O.E.M. to incorporate data collision detection.  If the code
>received differs from the code transmitted, the code can be assumed to have
>been corrupted by noise (or another transmission) on the powerline."  The
>fact that the XTB-II does not return any message when there is an error
>meets that condition.

That's a problem. ADI did this initially with the first few CPU-XAs but I
caught it and they fixed it early on. You need to report the errors when
they form valid X-10 codes (almost always from collisions) as X-10 receivers
will respond to the erroneous codes if they happen to be for their address
or housecode. The TW523 will report them.

There may also be a problem with the way you determine good/bad. Just
checking for nine 1s isn't adequate. You need to check that there are no
runs of three consecutive 1s or 0s.

It should be noted that since the TW523 delays its output for 22 half-cycles
its impossible to avoid collisions or to practice "polite" transmissions
when using it. All that can be done is to detect collisions after the fact.

In your case, you can monitor the powerline and stop transmitting when you
see a 1 when sending a 0. This is how the CM11A and CM15A operate. While the
first copy of any code may be corrupted, the second copy will be OK. You can
then retransmit once the line is clear.

Also, off the top of my head, I think the Ocelot/Leopard will report the
first part of the extended code but I may be confused from staring at
roZetta's output screens for a few hours.

http://www.davehouston.net
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