Compaq EV68A specifications Dcokh

21264/EV68A Signal Names and Functions

Table 3–2 21264/EV68A Signal Descriptions (Continued)

Signal	Type	Count	Description
BcDataOutClk_H[3:0]	O_PP	8	Bcache data output clocks. These free-running clocks are dif-
BcDataOutClk_L[3:0]			ferential copies of the Bcache clock and are derived from the
			21264/EV68A GCLK. Their period is a multiple of the GCLK
			and is fixed for all operations. They can be configured so that
			their rising edge lags BcAdd_H[23:4] by 0 to 2 GCLK cycles.
			The 21264/EV68A synchronizes tag output information with
			these clocks.
BcDataWr_L	O_PP	1	Bcache data write enable. The 21264/EV68A asserts this signal
			when writing data to the Bcache data arrays.
BcLoad_L	O_PP	1	Bcache burst enable.
BcTag_H[42:20]	B_DA_PP	23	Bcache tag bits.
BcTagDirty_H	B_DA_PP	1	Tag dirty state bit. During cache write operations, the 21264/
			EV68A will assert this signal if the Bcache data has been mod-
			ified.
BcTagInClk_H	I_DA	1	Bcache tag input clock. The 21264/EV68A uses this input
			clock to latch the tag information on Bcache read operations.
			This clock is used with high-speed SDRAMs, such as DDRs,
			that provide a clock-out with data-output pins to optimize
			Bcache read bandwidths. The 21264/EV68A internally syn-
			chronizes the data to its logic with clock forward receive cir-
			cuits similar to the system interface.
BcTagOE_L	O_PP	1	Bcache tag output enable. This signal is asserted by the 21264/
			EV68A for Bcache read operations.
BcTagOutClk_H	O_PP	2	Bcache tag output clock. These clocks “echo” the clock-for-
BcTagOutClk_L			warded BcDataOutClk_x[3:0] clocks.
BcTagParity_H	B_DA_PP	1	Tag parity state bit.
BcTagShared_H	B_DA_PP	1	Tag shared state bit. The 21264/EV68A will write a 1 on this
			signal line if another agent has a copy of the cache line.
BcTagValid_H	B_DA_PP	1	Tag valid state bit. If set, this line indicates that the cache line
			is valid.
BcTagWr_L	O_PP	1	Tag RAM write enable. The 21264/EV68A asserts this signal
			when writing a tag to the Bcache tag arrays.
BcVref	I_DC_REF	1	Bcache tag reference voltage.
ClkFwdRst_H	I_DA	1	Systems assert this synchronous signal to wake up a powered-
			down 21264/EV68A. The ClkFwdRst_H signal is clocked
			into a 21264/EV68A register by the captured FrameClk_x
			signals. Systems must ensure that the timing of this signal
			meets 21264/EV68A requirements (see Section 4.7.2).
ClkIn_H	I_DA_CLK	2	Differential input signals provided by the system.
ClkIn_L
DCOK_H	I_DA	1	dc voltage OK. Must be deasserted until dc voltage reaches
			proper operating level. After that, DCOK_H is asserted.
EV6Clk_H	O_PP_CLK	2	Provides an external test point to measure phase alignment of
EV6Clk_L			the PLL.

3–4 Hardware Interface 21264/EV68A Hardware Reference Manual