communication channel of Q-bus is Q1 NBP protocol
1 Mbps (unformatted) serial bus with substantial transfer
support of DMA controllers in both ends of transmission
path. Q2 bus is spare and is in service when Q1 faults. Q3
bus supports mutual precise synchronization of control
computer of the bogie converters. The precise
synchronization is necessary to minimize the trolley
current ripple of main drives.