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JTAG Pull-up/Pull-down

Started by georgeioak November 21, 2006
Hello Everyone:

We just started working on our first design based on the LPC2101 part.
We have a Keil MDB2103 Eval Board and followed the reference design
schematic for the JTAG interface which showed TCK and RTCK being
pulled down. We had nothing but troubles trying to get the ULINK JTAG
adapter communicating and only after we changed these 2 signals to
being pull-ups did we successfully communicate and download our code.

We had a few other problems going on and haven't gone back since we
got everything working but I thought I would post a question and see
what others are doing to there JTAG signals and if the schematic is
incorrect from Keil.

Thanks,
George

An Engineer's Guide to the LPC2100 Series

I beg to differ, KEIL schematic is correct.
It is as ARM Ltd. says it ought to be:

http://www.arm.com/support/faqdev/1277.html

Perhaps something else is going on with your design?
BTW, it may work either way, as long as TCK/RTCK do not float.
Roger

--- In l..., "georgeioak" wrote:
>
> Hello Everyone:
>
> We just started working on our first design based on the LPC2101 part.
> We have a Keil MDB2103 Eval Board and followed the reference design
> schematic for the JTAG interface which showed TCK and RTCK being
> pulled down. We had nothing but troubles trying to get the ULINK JTAG
> adapter communicating and only after we changed these 2 signals to
> being pull-ups did we successfully communicate and download our code.
>
> We had a few other problems going on and haven't gone back since we
> got everything working but I thought I would post a question and see
> what others are doing to there JTAG signals and if the schematic is
> incorrect from Keil.
>
> Thanks,
> George
>
OK then, how about P0.14, that also needs a pull-up too, right? Any
other signals that we need to be aware of in order to program the
part through JTAG?

--- In l..., "roger_lynx" wrote:
>
> I beg to differ, KEIL schematic is correct.
> It is as ARM Ltd. says it ought to be:
>
> http://www.arm.com/support/faqdev/1277.html
>
> Perhaps something else is going on with your design?
> BTW, it may work either way, as long as TCK/RTCK do not float.
> Roger
>
> --- In l..., "georgeioak" wrote:
> >
> > Hello Everyone:
> >
> > We just started working on our first design based on the LPC2101
part.
> > We have a Keil MDB2103 Eval Board and followed the reference
design
> > schematic for the JTAG interface which showed TCK and RTCK being
> > pulled down. We had nothing but troubles trying to get the ULINK
JTAG
> > adapter communicating and only after we changed these 2 signals
to
> > being pull-ups did we successfully communicate and download our
code.
> >
> > We had a few other problems going on and haven't gone back since
we
> > got everything working but I thought I would post a question and
see
> > what others are doing to there JTAG signals and if the schematic
is
> > incorrect from Keil.
> >
> > Thanks,
> > George
>
--- In l..., "georgeioak" wrote:
>
> OK then, how about P0.14, that also needs a pull-up too, right? Any
> other signals that we need to be aware of in order to program the
> part through JTAG?

It's probably best to copy another design like:
http://www.olimex.com/dev/images/lpc-h2103-sch.gif

It's not a 2101 but it should get you started. I didn't look to see
if there are differences between the 2101 and the 2103. See the User
Manual.

Richard

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