FAQ:Programming CVs over 255 with an NCE Power Pro
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It is not possible to program a CV higher than 255 using a Power Pro DCC System by NCE. This answer pertains to the Power Pro, not the Power Cab.
Attempting to do so may corrupt a multifunction decoder.
There is an issue within the firmware used by the Power Pro. The firmware lacks the ability to trap a value greater than 255. The issue is that the firmware is truncating the most significant bit. A value of 256 is equal to 2^8 in Binary (See note).
The firmware ignores this bit, only seeing 8 bits (numbered 0-7, maximum decimal value of 255). If a value such as 256 is entered, it sees the first eight bits as having values of zero. Attempting to write to CV285 results in CV29 being altered (285 –256 = 29).
Software such as JMRI DecoderPro has internal logic to trap any write attempts to CVs over 255. Some multifunction decoders may have workarounds in their firmware to prevent these issues.
Note:
The maximum value contained in one byte (eight bits) is 255, represented by the hexadecimal value of FF. The value of 256 is equal to 100 in hex. By truncating the most significant bit, the resulting value is 00.