Quote Originally Posted by NomakeWan View Post
... when I do that, I do not see the transmission. None of it. Not a single byte from the Mega shows up in EEHack's idle scan. So it's not that the CCM isn't reading the whole message and thus the checksum isn't matching...it's that the message does not appear on the line at all.
So you most likely have an issue with your circuit. Try the diode and resistor arrangement and see what happens while running an idle scan. Doesn't need to be a zener - any diode will do the trick just make sure the cathode (stripe) is pointing towards the arduino TX pin.

Nice work steveo. Is there anything I can test that you haven't already?

Code:
COMM::Sent message: F1580370CA7A
COMM::Recieved reply: F15703FEB7
CCM Software unlock: NO
COMM::Sent message: F15803644B05
COMM::Recieved reply: F157032293
CCM Hardware unlock: YES
Very elegant, checking if there will be a problem before requesting an unlock.