Reply by Lasse Langwadt Christensen●February 3, 20042004-02-03
Andrew Greensted wrote:
> Just for anyone who searches in the future.
> It seems that TDI and TMS are usually pulled high within target devices,
> however externally pulling them high (4.7k) is probably a good idea. TCK
> and TDO can be left floating.
>
> This may help:
> http://support.xilinx.com/xlnx/xil_ans_display.jsp?getPagePath=11433
>
> Andrew Greensted wrote:
>
>> Hi All,
>> I'm building a JTAG chain demultiplexer so I can control 30 identical
>> JTAG chains from a single point.
>> Can anyone confirm the quiescent (not doing anything) states of the
>> JTAG pins; so I know what to hold the pin levels at when a chain is
>> not being used.
>> I see that TMS, TCK & TDI have internal pull-ups, so would I place a
>> logical 1 on these when they're not in use? TDO is easy enough to sort
>> out as it just goes high Z.
>>
>> Many Thanks
>> Andy
>>
>
>
Making sure TMS stays high is a good idea, because them any glitches on
TCK will just keep (or get) the TAP controller in reset state
-Lasse
Reply by ●February 3, 20042004-02-03
Just for anyone who searches in the future.
It seems that TDI and TMS are usually pulled high within target devices,
however externally pulling them high (4.7k) is probably a good idea. TCK
and TDO can be left floating.
This may help:
http://support.xilinx.com/xlnx/xil_ans_display.jsp?getPagePath=11433
Andrew Greensted wrote:
> Hi All,
> I'm building a JTAG chain demultiplexer so I can control 30 identical
> JTAG chains from a single point.
> Can anyone confirm the quiescent (not doing anything) states of the JTAG
> pins; so I know what to hold the pin levels at when a chain is not being
> used.
> I see that TMS, TCK & TDI have internal pull-ups, so would I place a
> logical 1 on these when they're not in use? TDO is easy enough to sort
> out as it just goes high Z.
>
> Many Thanks
> Andy
>
--
Andrew Greensted Department of Electronics
Bio-Inspired Engineering University of York, UK
Tel: +44(0)1904 432379 Mailto: ajg112@ohm.york.ac.uk
Fax: +44(0)1904 433224 Web: www.bioinspired.com
Reply by ●February 2, 20042004-02-02
Hi All,
I'm building a JTAG chain demultiplexer so I can control 30 identical
JTAG chains from a single point.
Can anyone confirm the quiescent (not doing anything) states of the JTAG
pins; so I know what to hold the pin levels at when a chain is not being
used.
I see that TMS, TCK & TDI have internal pull-ups, so would I place a
logical 1 on these when they're not in use? TDO is easy enough to sort
out as it just goes high Z.
Many Thanks
Andy
--
Andrew Greensted Department of Electronics
Bio-Inspired Engineering University of York, UK
Tel: +44(0)1904 432379 Mailto: ajg112@ohm.york.ac.uk
Fax: +44(0)1904 433224 Web: www.bioinspired.com