FYI note*** - Since the Power Cab only has two wires to the track and no dedicated programming track output, those two wires are "hot" at all times.
You are only changing the "mode" that the Power Cab is operating in. This applies regardless of how the Power Cab is being used and if a USB interface is being used.
Service Mode Programming - Service Mode includes a CV Read back capability. The decoder can be read and its settings determined. Not all command stations support read back.
There are three methods of service mode programming:
Paged Mode This mode is the most commonly used programming mode and is the preferred method. It is very slow when reading back the CVs.
To read a CV, a number is sent to the decoder. If the response is negative, the number is incremented by one, and the process repeats until a positive response is received from the decoder. This process can repeat up to 256 times. Reading the complete CV set of a decoder will take a long time. Every CV will be tested sequentially in this manner.
Direct Mode is becoming more popular. Faster Read back of CVs. Instead of asking "Is it 1?, Is it 2?", Direct Mode takes a different approach. It asks if Bit 1 of the CV is set. Then "Is Bit 2 set?" Instead of making up to 256 inquiries to determine the value of a CV, it can do it with eight. It can read the entire decoder's CVs very quickly
Physical Register Mode (Recovery Mode) is an older, obsolete method of programming that is not used in current production decoders. This mode allows you to program a decoder no matter what state it is in. You do not even need to know the address (hence the danger of programming all your decoders at once). It will also work if the decoder's memory has become corrupted.