Compaq EV68A specifications Introduction to the External Interfaces

Models: EV68A

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Introduction to the External Interfaces

The Bcache interface includes a 128-bit bidirectional data bus, a 20-bit unidirec- tional address bus, and several control signals.

The BcDataOutClk_x[3:0] clocks are free-running and are derived from the internal GCLK. The period of BcDataOutClk_x[3:0] is a programmable mul- tiple of GCLK.

The Bcache turns the BcDataOutClk_x[3:0] clocks around and returns them to the 21264/EV68A as BcDataInClk_H[7:0]. Likewise, BcTagOutClk_x returns as BcTagInClk_H.

The Bcache interface supports a 64-byte block size.

The system interface includes a 64-bit bidirectional data bus, two 15-bit unidirectional address buses, and several control signals.

The SysAddOutClk_L clock is free-running and is derived from the internal GCLK. The period of SysAddOutClk_L is a programmable multiple of GCLK.

The SysAddInClk_L clock is a turned-around copy of SysAddOutClk_L.

Figure 4–1shows a simplified view of the external int erface. The function and purpose of each signal is described in Chapter 3.

4–2

Cache and External Interfaces

21264/EV68A Hardware Reference Manual

Page 90
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Compaq EV68A specifications Introduction to the External Interfaces