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Simplified Bus Arbitration Logic

IP.com Disclosure Number: IPCOM000039383D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01

Publishing Venue

IBM

Related People

Authors:
Frazier, GR [+details]

Abstract

A Small Computer System Interface (SCSI) bus arbitration process includes the following steps. Any device attempting to connect to a target device must execute these steps. 1. Wait for bus-free phase. 2. Turn on BUSY signal and Initiator's identification (ID) bit. 3. If a higher priority ID bit is one, release all signals and return to 1. 4. Turn on SELECT signal and Target's ID bit. 5. Release the BUSY signal. 6. Wait for Target to reassert BUSY 7. Turn off select After these steps, a connection between the target and initiator has been established. Steps 1-3 must be accomplished in less than 2 microseconds and therefore must be implemented with hardware. For devices with the highest ID bit, however, step 3 can be skipped.