[SI-LIST] : A timing question in high speed bus
=?gb2312?B?wfXK97Hy?= (liushb@263.net)
Tue, 17 Nov 1998 11:16:46 +0800
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Dear list,
I have to design a backplane bus with about 100M Hz clock and the =
transmission distance wanted as long as it can, using GTL . The design =
is to be a Synchronous clock one . The component we want to use as =
transceiver is SN74GTL16622, the specification said that it can function =
up to 200 Mhz clock frequency .
But I have a puzzle about the high speed bus's timing:=20
You know, the formula: "TFLT_MAX <=3DClock Period - TCO_MAX - TSU_MIN =
-CLKSKEW- CLKJITTER"(TFLT_MAX is the largest flight time a network will =
experience under all variation of conditions,TCO_MAX is the maximum =
colok to output specification, TSU_MIN is the minimum required time =
specified to setup before the clock,CLKJITTER is the maximum clock edge =
to edge variation,CLKSKEW is the maximum variation between components =
receiving the same clock edge.) For 100MHz bus,the Clock Period is 10ns, =
and for TI's SN74GTL16622,TCO_MAX is 6.1ns (maximum of TPLH from CLKAB =
to B is 6.1ns),TSU_MIN is 2.6ns. In some papers such as Intel's Pentium =
II Processor GTL+ Guidelines, they give the CLKSKEW and CLKJITTER is =
about 0.4ns and 0.25ns. Then the TFLT_MAX is about only 0.65ns.=20
It's clear that the flight time is not enough , for example, in the =
NESA's paper "An Innovative Distributed Termination Scheme for GTL =
Backplane Bus Designs", they used the GTL+ to implement 100MHz bus , the =
delay of 9 inches distance is 1.62ns (this delay time is not the =
flight time, it's just a part of it.), and my design have to be much =
longer than 9 inches . So I am puzzled , is the calculation wrong, or =
others?
How can I settle the timing question ?
(By the way, the maximum of TPLH from CLKAB to B is 6.1ns , how can it =
work on 200MHz clock frequency ?)
Thank you .
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Dear =
list,
I have to design a backplane bus with about 100M Hz clock and =
the=20
transmission distance wanted as long as it can, using GTL . The design =
is to be=20
a Synchronous clock one . The component we want to use as transceiver is =
SN74GTL16622, the specification said that it can function up to 200 Mhz =
clock=20
frequency .
But I have a puzzle about =
the high=20
speed bus's timing:
You know, the formula: "TFLT_MAX <=3DClock Period - TCO_MAX - TSU_MIN -CLKSKEW- CLKJITTER"(TFLT_MAX is the =
largest flight=20
time a network will experience under all variation of conditions,TCO_MAX is the maximum colok to output specification, =
TSU_MIN is the minimum required time specified to setup =
before the=20
clock,CLKJITTER is the maximum clock edge to edge=20
variation,CLKSKEW is the maximum variation between =
components receiving the same clock edge.) For 100MHz bus,the Clock =
Period is=20
10ns, and for TI's SN74GTL16622,TCO_MAX is 6.1ns =
(maximum of=20
TPLH from CLKAB to B is 6.1ns),TSU_MIN=20
is 2.6ns. In some papers such as Intel's Pentium II Processor GTL+ =
Guidelines,=20
they give the CLKSKEW and CLKJITTER is=20
about 0.4ns and 0.25ns. Then the TFLT_MAX is about =
only=20
0.65ns.
It's clear=20
that the flight time is not enough , for example, in the NESA's paper =
"An=20
Innovative Distributed Termination Scheme for GTL Backplane Bus =
Designs",=20
they used the GTL+ to implement 100MHz bus , the delay of 9 inches =
distance is 1.62ns (this delay time is not the flight time, it's =
just a=20
part of it.), and my design have to be much longer than 9 inches . =
So I am=20
puzzled , is the calculation wrong, or =
others?
How=20
can I settle the timing question ?
(By the way, the maximum of =
TPLH from CLKAB to B is 6.1ns , how can it work on 200MHz =
clock=20
frequency ?)
Thank you =
.
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