AMD AMD-K6-2/400 User Guide - Page 129
D[63:0] (Data Bus
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23542A/0-September 2000 Preliminary Information AMD-K6™-2E+ Embedded Processor Data Sheet 5.18 D[63:0] (Data Bus) Pin Attribute Summary Driven, Sampled, and Floated Bidirectional D[63:0] represent the processor's 64-bit data bus. Each of the eight bytes of data that comprise this bus is qualified as valid by its corresponding byte enable. See "BE[7:0]# (Byte Enables)" on page 100. As Outputs: For single-transfer write cycles, the processor drives D[63:0] with valid data one clock edge after the clock edge on which ADS# is asserted and D[63:0] remain in the same state until the clock edge on which BRDY# is sampled asserted. If the cycle is a writeback-in which case four 8-byte transfers occur-D[63:0] are driven one clock edge after the clock edge on which ADS# is asserted and are subsequently changed off the clock edge on which each BRDY# assertion of the burst cycle is sampled. If the assertion of ADS# represents a pipelined write cycle that follows a read cycle, the processor does not drive D[63:0] until it is certain that contention on the data bus will not occur. In this case, D[63:0] are driven the clock edge after the last expected BRDY # of the previous cycle is sampled asserted. As Inputs: During read cycles, the processor samples D[63:0] on the clock edge on which BRDY# is sampled asserted. The processor always floats D[63:0] except when they are being driven during a write cycle as described above. In addition, D[63:0] are floated off the clock edge that BOFF # is sampled asserted and off the clock edge that the processor asserts HLDA in recognition of HOLD. Chapter 5 Signal Descriptions 107