[SI-LIST] Effect of Stub-Length on Max. Length Calculation
- From: "Adeel Malik" <adeelm@xxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 15 Nov 2002 16:08:01 +0500
Hi Experts,
In order to calculate the maximum length of the bus signals
(address, control and data) to meet the set-up and hold times, the
calculation usually starts with a formula such as :
tflight_time < tperiod - tco - treceiver_setup - tcrosstalk - tjitter
where tco is clock to output delay.
If we consider a following bus with a single driver and several receivers
and assuming that the bus employs 'Reflective Switcing' mechanism,
Driver---Receiver1---Receiver2--------------Receiver3
One needs to find the round-trip delay for a signal to travel from driver to
Receiver3 and back all the way and then calculate the max. allowable trace
length by allowing 5 to 10 round trips for a bus to quiet down.
So let say if we change the scenario a little bid and add some fixed length
stub close to Receiver 3 (for the purpose of adding the Test Point). So the
modified figure will now be:
< A >
Driver---Receiver1---Receiver2-------------Receiver3
|
|
|
| --> a stub of length L
|
|
TEST POINT CONNECTOR
My question is that how our original calculation to determine the max.
bus-length will be affected by the addition of this stub of length L. If the
length L is less than or equal to distance 'A' as depicted in the figure,
shouldn't our original estimation of the max. bus length remain valid ?.
Regards,
Adeel
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