Compaq 21264 Hardware Reference Manual page 72

21264/EV67 Signal Names and Functions
Table 3–2 21264/EV67 Signal Descriptions (Continued)
Signal
BcDataOutClk_H[3:0]
BcDataOutClk_L[3:0]
BcDataWr_L
BcLoad_L
BcTag_H[42:20]
BcTagDirty_H
BcTagInClk_H
BcTagOE_L
BcTagOutClk_H
BcTagOutClk_L
BcTagParity_H
BcTagShared_H
BcTagValid_H
BcTagWr_L
BcVref
ClkFwdRst_H
ClkIn_H
ClkIn_L
DCOK_H
EV6Clk_H
EV6Clk_L
Hardware Interface
3–4
Type Count Description
O_PP 8 Bcache data output clocks. These free-running clocks are dif-
ferential copies of the Bcache clock and are derived from the
21264/EV67 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/EV67 synchronizes tag output information with
these clocks.
O_PP 1 Bcache data write enable. The 21264/EV67 asserts this signal
when writing data to the Bcache data arrays.
O_PP 1 Bcache burst enable.
B_DA_PP 23 Bcache tag bits.
B_DA_PP 1 Tag dirty state bit. During cache write operations, the 21264/
EV67 will assert this signal if the Bcache data has been modi-
fied.
I_DA 1 Bcache tag input clock. The 21264/EV67 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/EV67 internally synchronizes the
data to its logic with clock forward receive circuits similar to
the system interface.
O_PP 1 Bcache tag output enable. This signal is asserted by the 21264/
EV67 for Bcache read operations.
O_PP 2 Bcache tag output clock. These clocks "echo" the clock-for-
warded BcDataOutClk_x[3:0] clocks.
B_DA_PP 1 Tag parity state bit.
B_DA_PP 1 Tag shared state bit. The 21264/EV67 will write a 1 on this sig-
nal line if another agent has a copy of the cache line.
B_DA_PP 1 Tag valid state bit. If set, this line indicates that the cache line
is valid.
O_PP 1 Tag RAM write enable. The 21264/EV67 asserts this signal
when writing a tag to the Bcache tag arrays.
I_DC_REF 1 Bcache tag reference voltage.
I_DA 1 Systems assert this synchronous signal to wake up a powered-
down 21264/EV67. The ClkFwdRst_H signal is clocked into
a 21264/EV67 register by the captured FrameClk_x signals.
Systems must ensure that the timing of this signal meets
21264/EV67 requirements (see Section 4.7.2).
I_DA_CLK 2 Differential input signals provided by the system.
I_DA 1 dc voltage OK. Must be deasserted until dc voltage reaches
proper operating level. After that, DCOK_H is asserted.
O_PP_CLK 2 Provides an external test point to measure phase alignment of
the PLL.
Alpha 21264/EV67 Hardware Reference Manual