Re: [SI-LIST] : Daisy-Chain

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From: S. Weir ([email protected])
Date: Mon Mar 20 2000 - 00:47:45 PST


If you require a monotonic waveform at all loads, because this is some
clock or other strobe, then you must:

1. Have a driver with an impedance that is low compared to the
characteristic Z of the line.
2. Be free of excessive lumped capacitance on the line, especially in the
3. End terminate the line by a method that is acceptable for the trace
length, and driver:
         a. Resistor to Vtt
         b. Thevenin equivalent of resistor to Vtt.
         c. AC termination.
         d. Parallel termination to ground

A, b, and d all depend on how much power you can pump out of your driver.
The AC termination method works if the line is not long compared to the
minimum pulse duration.

It sounds as though your simulation is set with a strong driver, and heavy
capacitive load at point 2). If your routing puts a number of the loads
close to each-other, place them close to the end with the terminator.



At 05:26 PM 3/20/2000 +0900, you wrote:
>I have a trace which connects in daisy-chain from 1 driver(transceiver) to
>6 receivers ( 2 ASICs (BGA type), 2 ROMs, 1 flash memory and 1 transceiver).
>The connecting sequence is 1) ASIC1, 2) ASIC2, 3), transceiver, 4) ROM1,
>5) ROM2, 6) Flash memory.
>My problem is the simulation result shows reflection occurs at the
>receiver(non-monotonic waveform) nearest to the driver. Is it a good
>idea to put a pulldown resistor at that receiver(resistor value = Zo)?
>I welcome any suggestions or advices on this matter. Thank you.
>$B!!!!(BUltimate Technologies Inc.
> SI Group
> 1462-6F, Shindencho, Nagano-Shi 380-0835, Japan
>$B!!(B TEL$B!'(B $B!!(B026-267-7256
>$B!!!!(BFAX$B!'(B 026-267-7259

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