Demand driven access mechanism
AssigneeControl Data Corporation
InventorDavid A. Van Hatten
Life of this patent
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Abstract
A demand driven access mechanism comprises logic apparatus at each station capable of seizing use of a shared communication channel for enabling access to a selected one station. The logic apparatus receives status signals from all stations so that if one station seeks access to the channel it will be enabled immediately upon an inactive status to the channel. If two or more stations simultaneously seek access to the channel, the logic apparatus establishes a priority order between them, thereby enabling access to only one station at a time. The priority ordering is based, in part, by the identity of the station last enabled, to thereby assure priority order allocation among the stations.
Claims12
A demand driven access mechanism for enabling a station to seize use of a communication channel shared with one or more other stations, said mechanism comprising:
- first logic means responsive to a signal from said station for producing a station request signal if the station is either ready to seize use of the channel or is using the channel and for producing a station not-request signal if the station is neither ready to seize use of the channel nor is using the channel;
- second logic means for producing either an enable signal to said station or a not-enable signal, said second logic means being responsive to the station's enable signal and a request signal from a second station or to the stations's not-request signal and the stations's not-enable signal to produce said enable signal whenever the station is enabled by its respective second logic means and no request signal is present from the second station's first logic means or whenever the station's second logic means is not producing said enable signal and the station is ready to seize use of the channel.
In a communication system having a plurality of stations each capable of seizing use of a communications channel shared by said stations, the improvement comprising, at each station, a demand driven access mechanism for enabling the respective station to seize use of the channel, said mechanism comprising:
- A. first logic means responsive to the respective station for producing a station request signal whenever the respective station is either ready to seize use of the channel or is using the channel, and for producing a station not-request signal whenever the respective station is neither ready to seize use of the channel nor using the channel;
- B. second logic means for producing either an enable signal or a not-enable signal, said second logic means comprising
- (i) first AND gate means responsive to the respective station's enable signal and to a request signal from a second station to produce a first logic signal,
- (ii) second AND gate means responsive to the respective station's not-request and not-enable signal to produce a second logic signal,
- (iii) OR gate means responsive to either said first or second logic signals to produce a third logic signal;
- (iv) enable means responsive to said third logic signal to produce said not-enable signal and responsive to the absence of said third logic signal to produce said enable signal;
- and
- C. output means for providing said enable signal to the respective station.
Dependencies are inferred from the claim text.