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Re: TDI and TDO signal



Hi All,

This is one area of PCI that has confused me, perhaps someone can clarify.  Is
there some type of specification, that mechanically, a PCI socket will keep
TDI and TDO connected when a PCI card is not present?  If not, then
I'm not convinced that connecting TDI and TDO together is the proper
solution, either.  It would appear to me that PCI slots that are not populated 
would make TDI and TDO appear open, so even if you connect TDI and TDO together 
in your card, there's still an incomplete scan path when the system is not fully 
populated with PCI cards.  

However, by connecting TDI and TDO together on your card, you have made your card
incompatible in systems supporting a 1149.1 multidrop architecture.   In a multidrop 
architecture, the TDI, TDO, TMS and TCK are common to all daughter boards in the system.  
Each daughter board requires a multi-drop interface chip (see TI '8996 addressable 
shadow port or similar) in order to address the daughter boards in the system and select
which board will drive on TDO during the SHIFT-DR or SHIFT-IR states of 1149.1.  
One advantage would be that not all slots need to be populated to complete the scan 
chain.

Regards,
CJ 
IEEE 1149.1 working group member (however, these are my personal opinions and
not the opinion of the working group)



>>
>>In <199608210937.CAA12145@scruz.net> "John R Pierce"
><uunet!scruznet.com!pierce> writes:
>>>Read the PCI 2.1 SPEC.  Those books are not the SPECIFICATION.
>>
>>>But, yes, you hook them up.  otherwise other boundary scan boards would
>fail if
>>>the system supported boundary scans...
>>
>>>-jrp
>>>(btw, your email address is broken, '@@' don't work!)
>>
>>>----------
>>>> From: Carsten Bode <cb@@Diehl.DE>
>>>> To: Mailing List Recipients <pci-sig-request@znyx.com>
>>>> Subject: TDI and TDO signal
>>>> Date: Wednesday, August 21, 1996 4:56 AM
>>>> 
>>>> Hello
>>>> I have a simple question regarding the design of a PCI card ( standard PC
>>>format ) that does not
>>>> support boundary scan.
>>>> Should I connect TDI and TDO or leave them open or pull them up or down with
>>>a resistor?
>>>> 
>>>> I found different statements in the Mindshare PCI book ( connect TDI and TDO
>>>) and
>>>> the PCI book from Ed Solari ( recommends 5K pullups/pulldowns on various
>T...
>>>signals ).
>>>> 
>>>> Regards,
>>>>  Carsten Bode
>>>> 
>>
>>
>>
>>-- 
>>My email: cjclark@intellitech.com
>>------------------------------------------------------------------------
>>+ Intellitech Corporation                     Scan Tools               +
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>>
>>

>--------------------------------
>  Alan Deikman, ZNYX Corporation
>  alan@znyx.com


>End of forwarded message.

>-- 
>My email: cjclark@intellitech.com
>------------------------------------------------------------------------
>+ Intellitech Corporation                     Scan Tools               +
>+ 66 Route 25, Meredith, NH 03253        for Design and Test.          +
>+ PH:603-279-6308 FX:603-279-5135     For info: info@intellitech.com   +
>------------------------------------------------------------------------


-- 
My email: cjclark@intellitech.com
------------------------------------------------------------------------
+ Intellitech Corporation                     Scan Tools               +
+ 66 Route 25, Meredith, NH 03253        for Design and Test.          +
+ PH:603-279-6308 FX:603-279-5135     For info: info@intellitech.com   +
------------------------------------------------------------------------
al\