User`s guide

The XMI

The Read transactions consist of a command transfer followed by a

return data transfer, as shown in Figure 2–24. The two transfers are

the command (FUNCT = CMD) and the read data response (FUNCT =

GRD0). The commander arbitrates for the bus in cycle 0 and wins. In

cycle 1, it drives the function, command, address of the read, and its own

ID (for later use to identify the returning data). In cycle 3, the responder

conﬁrms receipt of the information.

Some variable time later, in this example at cycle 4, the return data

transfer begins with the responder arbitration for the bus. Having won it,

the responder drives the function, the data, and the commander’s ID in

cycle 5. The status of the returning data is speciﬁed in the read response

function code, either Good Read Data, Corrected Read Data, or Read Error

Response. The commander monitors the bus, checking for an ID match

during read data cycles to indicate that the read data is meant for that

commander.

If the particular transaction requested had been an Interlock Read, and if

the memory was already interlocked, the responder would have provided a

Locked Response (LOC) in place of the returned data. (See Figure 2–25.)

Figure 2–25 Interlock Read Transaction to a Locked Location

0 123 4567

FUNCT

DATA

CONF

ARB

|CMD | |

|LOC | |

... |

|CMDR|

|IREAD|

|CMDR |

|ACK |

| |RESP|

|CMDR|

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