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Alpha 21264/EV67 Hardware Reference Manual
Initialization and Configuration 7–7
Power-Up Reset Flow and the Reset_L and DCOK_H Pins
As BiST completes, the TestSt at_H pin is held low for 16 GCLK cycles. Then, if BiST
succeeds, the pin remains low. Otherwise, it is asserted. After successfully completing
BiST, the 21264/EV67 then performs the SROM load sequence (described in Chapter
11). After the SROM load sequence is finished, the 21264/EV67 deasserts SromOE_L.
7.1.5 Clock Forward Reset and System Interface Initialization
After the deassertion of SromOE_L, the reset state machine enters the
WAIT_ClkFwdRst1 state, where the 21264/EV67 waits for the system to deassert
ClkFwdReset_H. The 21264/EV67 samples the deasserting edge of ClkFwdReset_H
to take synchronous actions. It uses this synchronous event to reset the clock forward-
ing interface, start the outgoing clocks, and deassert internal reset. The chip then waits
264 cycles before issuing commands. The reset state machine is then in RUN and the
21264/EV67 begins fetching code at address 0x780.
Table 7–4 lists signals relevant to the power-up flow, provides a short description of
each, and any relevant constraints.
Table 7–4 Power-Up Flow Signals and Their Constraints
Signal Name Description Constraint
ClkIn_x Differential clocks that are
inputs to PLL or are
bypassed onto GCLK
directly
Clocks must be running before DCOK_H is
asserted.
PLL_VDD
VDD supply to PLL PLL_VDD must lead VDD.
VDD VDD supply to the 21264/
EV67 chip logic (except
PLL)
—
DCOK_H Logic signal to the 21264/
EV67 that the VDD supply
is good
—
Reset_L RESET pin asserted by
SYSTEM to the 21264/
EV67
Reset_L must be asserted prior to DCOK_H and
must remain asserted for at least 100 ms after
DCOK_H is asserted. This allows for PLL settling
time. Deassertion of Reset_L causes the 21264/
EV67 to ramp divisors to their final value and begin
BiST.
ClkFwdRst_H
Deassertion #1
Signal asserted by SYS-
TEM to synchronously
commence built-in self-test
and SROM load
ClkFwdRst_H must be deasserted after PLL has
achieved its lock in its final divisor value (about 20
µs). The deassertion causes built-in self-test to
begin on an internal clock cycle that corresponds to
one framing clock cycle after ClkFwdRst_H is
deasserted. ClkFwdRst_H can be asserted after
one frame clock cycle. See Figure 7–1.
ClkFwdRst_H
Deassertion #2
Signal asserted by SYS-
TEM to initialize and reset
clock forwarding interfaces
ClkFwdRst_H must be deasserted when the Cbox
has loaded configuration information. This occurs
as the first part of the serial ROM load, after BiST
is run. Once ClkFwdRst_H is deasserted, the
interface is initialized and can receive probe
requests from the 21264/EV67.