鈥?/div>
Clock Distribution for PowerPC鈩?620 L2 Cache
2 Selectable LVCMOS/LVTTL Clock Inputs
500ps Maximum Output鈥搕o鈥揙utput Skew
Drives Up to 18 Independent Clock Lines
Maximum Output Frequency of 110MHz
Synchronous Output Enable
Tristatable Outputs
32鈥揕ead TQFP Packaging
3.3V VCC Supply Voltage
FA SUFFIX
32鈥揕EAD TQFP PACKAGE
CASE 873A鈥?2
With an output impedance of approximately 7鈩? in both the HIGH and
LOW logic states, the output buffers of the MPC947 are ideal for driving
series terminated transmission lines. More specifically, each of the 9
MPC947 outputs can drive two series terminated 50鈩?transmission lines.
With this capability, the MPC947 has an effective fanout of 1:18 in
applications using point鈥搕o鈥損oint distribution schemes. With this level of
fanout, the MPC947 provides enough copies of low skew clocks for high
performance synchronous systems, including use as a clock distribution
chip for the L2 cache of a PowerPC 620 based system.
Two independent LVCMOS/LVTTL compatible clock inputs are available. Designers can take advantage of this feature to
provide redundant clock sources or the addition of a test clock into the system design. With the select input pulled HIGH, the
TTL_CLK1 input will be selected.
All of the control inputs are LVCMOS/LVTTL compatible. The MPC947 provides a synchronous output enable control to allow
for starting and stopping of the output clocks. A logic high on the Sync_OE pin will enable all of the outputs. Because this control
is synchronized to the input clock, potential output glitching or runt pulse generation is eliminated. In addition, for board level test,
the outputs can be tristated via the tristate control pin. A logic LOW applied to the Tristate input will force all of the outputs into
high impedance. Note that all of the MPC947 inputs have internal pullup resistors.
The MPC947 is fully 3.3V compatible. The 32鈥搇ead TQFP package was chosen to optimize performance, board space and
cost of the device. The 32鈥搇ead TQFP has a 7x7mm body size with a conservative 0.8mm pin spacing.
PowerPC is a trademark of International Business Machines Corporation.
1/97
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Motorola, Inc. 1997
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