Compaq EV68A specifications Clock Forwarding and System Clock Ratio Configuration, Pllvdd

Power-Up Reset Flow and the Reset_L and DCOK_H Pins

Table 7–2 Signal Pin Reset State (Continued)

Signal	Reset State	Signal	Reset State
SysAddOut_L[14:0]	Initially, during power-up reset, state	SysDataOutValid_L	NA (input)
	is not defined. If not during power-
	up, preserves previous state. Then,
	after the clock forward reset period
	(as the external clocks start), signal
	driven to NZNOP until the reset
	state machine enters RUN, when it
	is driven to NOP.
SysAddOutClk_L	Tristated	SysFillValid_L	NA (input)
SysCheck_L[7:0]	Tristated	SysVref	NA
			(I_DC_REF)
SysData_L[63:0]	Tristated
Clocks
ClkFwdRst_H	NA (input)	FrameClk_x	NA (input)
ClkIn_H	NA (input)	PLL_VDD	NA
ClkIn_L			(I_DC_REF)
EV6Clk_H	NA (input)
EV6Clk_L
Miscellaneous
DCOK_H	Must be deasserted until dc voltage	Tck_H	NA (input)
	reaches proper operating level.
PllBypass_H	NA (input)	Tdi_H	NA (input)
Reset_L	NA (input)	Tdo_H	Unspecified
SromClk_H	Tristated	TestStat_H	Tristated
SromData_H	NA (input)	Tms_H	NA (input)
SromOE_L	Tristated	Trst_L	NA (input)

In addition, as power is being ramped, Reset_L must be asserted — this allows the 21264/EV68A to reset internal state. Once the target voltage levels are attained, sys- tems should assert DCOK_H. This indicates to the 21264/EV68A that internal logic functions can be evaluated correctly and that the power-up sequence should be contin- ued. Prior to DCOK_H being asserted, the logic internal to the 21264/EV68A is being reset and the internal clock network is running (either clocked by the PLL VCO, which is at a nominal speed, or by ClkIn_H, if the PLL is bypassed).

The reset state machine is in state WAIT_SETTLE.

7.1.2 Clock Forwarding and System Clock Ratio Configuration

When DCOK_H is asserted, the 21264/EV68A samples several pins and latches in some initialization state, including the value of the PLL Ydiv divisor, which specifies the ratio of the system clock to the internal clock (see Section 7.11.2.3), and enables the charge pump on the phase-locked loop.

7–4 Initialization and Configuration 21264/EV68A Hardware Reference Manual