The signals on the HDRA connectors are tracked between the socket on the underside and the plug on the top so that, for example, pin 1 connects to pin 1 and pin 2 to pin 2. That is, the signals are routed straight through.

Several signals on the HDRB connectors are rotated in groups of four between the connectors on the bottom and top of each module. This ensures that each processor (or other bus master device) on a module connects to the correct signals according to whether it is bus master 0, 1, 2, or 3. The ID for the bus master on a module is determined by the position of the module in the stack.

This signal rotation scheme is illustrated in Figure 5.8.

The example in Figure 5.8 shows how a group of four signals (labelled A, B, C, and D) are routed through the stack. Signal C is rotated as it passes up through the stack and is only utilized on module 2.

All four signals are rotated and used in a similar way, as follows:

For details of the signals on the HDRB connectors, see HDRB.