6.30  The arbiter FSM defined in Section 6.8 (Figure 6.72) may cause device 3 to never get serviced if devices 1 and 2 continuously keep raising requests, so that in the Idle state it always happens that either device 1 or device 2 has an outstanding request. Modify the proposed FSM to ensure that device 3 will get serviced, such that if it raises a request, the devices 1 and 2 will be serviced only once before the device 3 is granted its request.

               

6.31  Section 6.5 presents a design for the serial adder. Derive a similar circuit that functions as a serial subtractor which produces the difference of operands A and B. (Hint: Use the rule for finding 2’s complements in Section 3.3.1 to generate the 2’s complement of B.)