[SI-LIST] Re: source synchronous constraint

zanglinyuan,

What I understand from your statement is that data at the transmitter 
changes in an interval between +/- 1 ns around the output clock at the 
driver.  At the receiver it is required to be stable between +2.5 and 
-0.5ns around the input clock.  If , as in a normal source-synchronous 
system the clock is routed with equal delay to the data, then this will 
cause a timing violation at the receiver, which is correct.  The only 
way to counteract this problem is to delay the strobe by 1.5ns to 
compensate for the difference between the output delay and the input 
setup time.  This will also meet the hold time requirements.  This can 
be accomplished with an additional strobe trace length of about 9", 
assuming stripline trace on FR-4.

Please correct me if I misunderstand your question.

regards,

Scott

zanglinyuan wrote:

>Hi. Scott
>It is a typical source synchronous system .
>
>as follows:
>____                  _____
>|       |  strobe     |          |
>|       |------------|          |
>|TX  |                 |  RX  |
>|       | data         |          |
>|___ |----------- |_____|
>
>TX----transceiver
>RX----recevier 
>
>The TX parameter is the transceiver ouput  data relative to strobe.
>The  RX parameter is the receiver input requirement for data relative to 
>strobe.
>The strobe's active edge is rising edge.
>
>The key problem is the tranceiver ouput parameter does't match the receiver's 
>input requirement ,
>how to deal with  PCB'S routing ?
>
>(TX:setuptime=1ns,holdtime=1ns
>RX:setuptime=2.5ns,holdtime=0.5ns )
>
>
>thanks
>
> 
>----- Original Message ----- 
>From: Scott McMorrow <scott@xxxxxxxxxxxxx>
>To: <zanglinyuan@xxxxxxxxxx>
>Sent: Tuesday, August 27, 2002 12:23 PM
>Subject: Re: [SI-LIST] source synchronous constraint
>
>
>  
>
>>Zanglingyuan,
>>
>>It is not clear what your Tx parameters are.  Is this a double data rate 
>>source synchronous system where the setup and hold times are relative to 
>>the Tx strobe/clock?  If so, what edge of the strobe is the active edge. 
>> Are the Rx setup and hold parameters relative to the same strobe/clock 
>>edge?
>>
>>regards,
>>
>>scott
>>
>>
>>-- 
>>Scott McMorrow
>>Teraspeed Consulting Group LLC
>>2926 SE Yamhill St.
>>Portland, OR 97214
>>(503) 239-5536
>>http://www.teraspeed.com
>>
>>
>>zanglinyuan wrote:
>>
>>    
>>
>>>Hi:
>>>I am designing some source synchronous system,and need to make PCB routing 
>>>constraint.
>>>However,the timing parameter for tranceiver and reciever does not match each 
>>>other,
>>>for example :
>>>TX:setuptime=1ns,holdtime=1ns
>>>RX:setuptime=2.5ns,holdtime=0.5ns 
>>>
>>>even so,I don't think the system won't work if we just route the clk/data's 
>>>PCB length within
>>>some tolerance,because the datasheet does't give the valid data time which 
>>>is very important for
>>>the PCB constraint to be made.  
>>>
>>>what's the right way  to deal with such case? that's how to make the PCB 
>>>routing constraint for this case?
>>>
>>>Thanks a lot in advance.
>>>
>>>
>>>
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>>
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-- 
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com





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