Abstract: A bus device of a first type uses a first arbitration protocol. The first-type device is designed for use in a computer system having a communications bus, and one or more other bus devices connected to the bus, including possible first-type bus devices which also use the first arbitration protocol and one or more second-type bus devices which use a second, different, arbitration protocol. The first-type bus device includes a protocol specific memory for storing information; means for monitoring the bus to determine whether the current bus master of the bus arbitrated in the manner of the first or second arbitration protocols; and means for denying the current bus master the ability to access information stored in the protocol specific memory if the means for monitoring determines the bus master arbitrated according to the second arbitration protocol.

Abstract: A first-type bus device is designed for use in a computer system having one or more second-type bus devices. The second-type devices practice a round robin arbitration scheme, but the first type devices do not. According to the round-robin scheme, a second-type device which wins an arbitration asserts its ID on the system bus, each second-type device seeking to arbitrate compares its ID with that asserted by the current bus master, and uses that comparison to determine whether to assert its ID during arbitration in a high or low priority manner. The first-type bus device includes means for assuring that first-type and second-type devices never arbitrate at the same time. During arbitration, first-type devices only assert their ID number in one priority. Unlike second-type devices, they cannot assert their ID either in a high or low priority manner.

Abstract: A bus device of a first type is designed to work with a bus devices of a second type. A bus device of the second type, when it is a slave in a bus transaction, issues an ACK if it can respond to the command on time, a NO ACK if it can't respond at all, a STALL if it expects to be able to respond with only a short delay, and a RETRY if it expects to be able to respond, but only after a long delay. Slave Bus devices of the second type also monitor the length of time that they assert the STALL signal, and if they assert if for more than a predetermined period, they replace the STALL signal with a RETRY. Bus devices of the second type, when they are master in a bus transaction, respond to a NO ACK by terminating a transaction in one way and to a RETRY by terminating the transaction in a different way.