[SI-LIST] Re: SDRAM read problem

Dear Peter
my suggestion is to replace the series resistor near Processor with zero
ohm , then measure the   signal quality near to SDRAM, when processor
driving the signal , if signal quality is good , use series resistors near
to the SDRAM only  in next rev of PCB ,Normally SDRAM signal driving
capability is higher than processor (that depends on frequency of
operation) , select the SDRAM with respect ur required operational
frequency, don't go much higher than the requirement.


Thanks & Regards

Madakath Sumesh
Engineer - Hardware
SCM Microsystems (India) Private Limited
5th Floor, D Block South, Tidel Park
4, Canal bank Road,
Taramani, Chenna 600 113
India
Phone :+91-44-22540020
Fax      :+91-44-22540645
Web    : www.scmmicro.com

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             "Calvo, Oscar A                                               
             (FL51)"                                                       
             <Oscar.A.Calvo@ho                                          To 
             neywell.com>              peter.qiu@xxxxxx,                   
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                                       [SI-LIST] Re: SDRAM read problem    
             11/22/2005 02:28                                              
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Peter,

Sounds like you also need series terminations at the output of the SDRAM
before the lines go to the bus transceiver.

Oscar

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Qiu, Peter (GE Consumer & Industrial, consultant)
Sent: Friday, November 18, 2005 10:31 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] SDRAM read problem

Hi,=20

I have a embedded system with a microprocessor, a  SDRAM(SDR), and a bus =
transceiver chip reside on the data bus(behind the bus transceiver, =
there are other peripherals). They are in daisy-chain mode, i.e. the =
data bus signals from microprocessor first reach the SDRAM,  then go to =
the bus transceiver. I put the termination resistors close to the =
microprocessor side. During the write operation to the SDRAM, the signal =
quality is ok. While during the read from the SDRAM, the signal on the =
microprocessor side suffers excessive overshoot and undershoot. May I =
know what is the better solution to terminate this kind of bi-direction =
bus? if I also put the termination resistor near the SDRAM end, does it =
affect the read/write operation to the transceiver chip behind the =
SDRAM?  Thanks.
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