Re: [SI-LIST] : Daisy-Chain

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From: Jim Freeman (freeman@broadcom.com)
Date: Mon Mar 20 2000 - 11:22:21 PST


Another solution is a series termination at the driver. The transmission
line may be mismatched at the driver. This works best with
point-to-point signals. The existence of a transceiver on your path may
mean you have a bi-directional path.

Jim Freeman

"S. Weir" wrote:

> KT,
>
> 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 middle.
> 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.
>
> Regards,
>
>
> Steve.
>
>
> At 05:26 PM 3/20/2000 +0900, you wrote:
>
>> Hi,
>>
>> 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.
>>
>> Regards,
>> KT.THAM
>>
>>
>>
>>
>>
>> _________________________________________________________
>>
>> $B!!!!(BUltimate Technologies Inc.
>> SI Group
>> KT.THAM
>>
>> 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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