The CVs ranging from 257 – 511 have a special meaning on a LokSound decoder: They are “indexed”. This means, that the meaning of any of these CVs can change depending on the value of the so-called “Index register”. By changing the value of the index register, also the meaning and the value of the CV itself is changed. This method allows us to use every CV multiple times and results in a extension of available CVs.
The index register is CV 32. It can hold the values 0,1,2 or 3. You can write the index register at any time using any programming method. Based on the value of CV 32, the meaning of CV 257 – 511 is changed.
The meaning of all other CVs ( 1 – 256 ) is not influenced by the value of the index register.
So before you read or write any of the CVs located in the range of 257 – 511, please make sure that you set the index register to the correct value first.
see page 28 of the manual attached to this article