The functions of the NTCF22 prefix are: 2 as a positive call; 3 as a negative call; and A as a depository unit. The management depository of the in-place bus coupling unit, which records the order in which the data in the command table is used, records the use of the data words in the command table list in sequential order.

The two management bits of the NTCF22 indicate the use of the data words. If a data in the bus data storage area is a “source” that is to be output to the local bus, or a “destination” that is to receive data from the local bus, neither a “source” nor a “destination” is a “source” or a “destination” that is to receive data from the local bus, or a “source” or a “destination” that is to receive data from the local bus, the data word in the instruction list is used in order. Neither “source” nor “destination” is a unit that does not need to be exchanged.

The NTCF22 accesses this management bit memory during data exchange. After judging the information provided by the management bit and the status of the data received on the local bus (data received after the control system recognises the information), the local bus data is stored in the bus data storage area of the data storage device.