Intel Pentium Pro Family, Developer'S Manual, Page: 95 / 328

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BUS PROTOCOL
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A response that does not require the data bus (no data response, deferred response, retry
response, or hard failure response) may be driven even if DBSY# is active due to a
previous transaction.
On observation of active RS[2:0]# response, the Transaction Queues are updated and {rcnt} is
decremented.
4.6. DATA PHASE
4.6.1. Data Phase Overview
During the Data Phase, data is transferred between different bus agents. Data transfer responsi-
bilities are negotiated between bus agents as the transaction proceeds through various phases.
Based on the Request Phase, a transaction either contains a “request-initiated” (write) data trans-
fer, a “response-initiated” (read) data transfer, or no data transfer. On a modified hit during the
Snoop Phase, a “snoop-initiated” data transfer may be added to the request or substituted from
the response in place of the “response-initiated” data transfer. On a deferred completion re-
sponse in the Response Phase, “response-initiated” data transfer is deferred.
4.6.1.1. BUS SIGNALS
The bus signals driven in this phase are D[63:0]#, DEP[7:0]#, DRDY#, and DBSY#.
All Data Phase signals are bused.
4.6.2. Data Phase Protocol Description
4.6.2.1. SIMPLE WRITE TRANSFER
Figure 4-18 shows a simple write transaction (request-initiated data transfer). Note that the data
is transferred before the response is driven.