Re: [SI-LIST] : Daisy-Chain

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From: Jeff Reeve (jtreeve@foxinternet.net)
Date: Mon Mar 20 2000 - 09:28:09 PST


Normally just lurk...but would like to add my .02 here. I too have experienced the same phenomona in the past. The solution I wuold like to suggest is to end terminate using your favorite method (AC, thev. equiv, R to ground, etc.). But additionally put a resisistor of value Zo just before the net connects to each receiver. Your net should daisy chain to each of the resistors, the other side of the resistor connects to the receiver input pin. Provided you keep this "stub" as short as possible, I've found this to work well. Your trace will look like the following:

Driver -----------------------------------------------------------------------------End Term
                    R R R R R R
                   Pin Pin Pin Pin Pin Pin

I would be very curious to hear what the list has to say. I would also like to hear if this suggestion cleans up you simulation.

Regards
Jeff
  ----- Original Message -----
  From: Tham Kok Tong
  To: si-list@silab.eng.sun.com
  Cc: kt_tham@hotmail.com ; smtai@uti2000.co.jp
  Sent: Monday, March 20, 2000 12:26 AM
  Subject: [SI-LIST] : Daisy-Chain

  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

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