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29 September 1997 – Subject To Change
Electrical Data
9–5
Clocking Scheme
9.3 Clocking Scheme
The differential input clock signals osc_clk_in_h,l run at the internal frequency of
the time base for the 21164PC. The output signal cpu_clk_out_h toggles with an
unspecified propagation delay relative to the transitions on osc_clk_in_h,l.
The 21164PC provides a system clock to run the chip synchronous to the system.
The 21164PC generates and drives out a system clock, sys_clk_out1_h. It runs syn-
chronous to the system clock at a selected ratio of the internal clock frequency. There
is a small clock skew between the internal clock and sys_clk_out1_h.
Refer to Section 4.2 for more information on clock functions.
9.3.1 Input Clocks
The differential input clocks osc_clk_in_h,l provide the time base for the chip when
dc_ok_h is asserted. These pins are self-biasing, and must be capacitively coupled to
the clock source on the module.
Note:
It is not desirable to drive the osc_clk_in_h,l pins directly.
The terminations on these signals are designed to be compatible with system oscilla-
tors of arbitrary dc bias. The oscillator must have a duty cycle of 60%/40% or
tighter. Figure 9–1 shows the input network and the schematic equivalent of
osc_clk_in_h,l terminations.