RE: JTAG pins

["Olaf Birkeland" <Olaf.Birkeland@fast.no>]

> -----Original Message-----
> From: firlit@utmc.aeroflex.com [mailto:firlit@utmc.aeroflex.com]
> Sent: Friday, August 31, 2001 20:18
> To: pci-sig@znyx.com
> Subject: JTAG pins
>
>
> Hello,
>
> I have just recently come across a fairly new motherboard which has the
> PCI connector TMS signal pulled down to ground with a 1K resistance.
> This is crippling to my PCI card, since I use the JTAG signals for
> production test of the card (and this pulldown puts my PCI interface
> device into JTAG mode).  This brings me to 2 questions:
>
> 1.  Has anyone come across this problem and researched into the
> magnitude of it?  Are there few or many motherboards out there which are
> not compliant to the rev 2.2 spec, paragraph 4.3.3 -- requiring a pullup
> on TMS and TDI?

I've seen a lot of variation on this, ranging from incorrect pull-up/down to
no resistors at all.
>
> 2.  Are most PCI expansion cards designed without using the JTAG pins of
> the PCI connector, hence most cards operate fine in these non-compliant
> motherboards?

At least to my experience. I've opted for bringing JTAG out to a separate
connector in my designs, leaving the PCI JTAG as is (i.e. connecting TDI to
TDO). This makes my JTAG chain independent of whatever the motherboard and
other expansion cards are doing. The drawback is the need for a separate
test connector and plugging into this during production test.

Regards,
- Olaf