I understand now why you went to the effort of a proposal to them both regarding a change to the method.
The emonV3 sketch has not taken all possibilities into account it seems.
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The response on the Arduino forum:
You will seldom, if ever, see an actual Arduino "factory" response.
A search brings up three different threads on the Arduino forum suggesting 0xFF is meant to be the default.
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Checking for 0x00 or 0xFF is better I agree. Would there be a problem with backwards compatibility if 0x00 were used as a check?
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A signature check would be an easy-to-implement change and relatively fail-safe, but isn’t backwards compatible.