the local power manager 21 of a given functional block 15 may upon entry into the low power state de assert its respective physical interface signal when either of the physical interface signals is de asserted or when a corresponding software request is asserted link state machine 25 may respond by asserting the link unavailability signal thereby indicating that communications link 12 is currently unavailable furthermore the de assertion of a physical interface signal by either of the functional blocks 15 associated with a particular communications link 12 may result in link state machine 25 de asserting the corresponding combined indication at some point in time subsequent to the assertion of the link unavailability signal the local power managers 21 for functional blocks 15 a and 15 b may each assert respective acknowledgement signals u2018 link_un_ack_a u2019 and u2018 link_un_ack_b u2019 indicating acknowledgement of the unavailability of communications link 12 link state machine 25 in the embodiment shown may utilize these signals in determining when communications link 12 can be made available once again in particular link state machine 25 in the embodiment shown is configured to maintain assertion of the link unavailability signal until at least a time when it has received acknowledgement signals.