Lpc2000

> From: "Ben Dooks" <ben@...>
> On Thu, Nov 27, 2003 at 06:18:30PM -0000, leon_heller wrote:
> > I've just added the connection details for the Wiggler JTAG interface
> > for my LPC210x system to my web page:
> >
> > http://www.geocities.com/leon_heller/lpc2104.html
> >
> > Although I used 10k pull-up resistors on the inputs from the Wiggler,
> > I don't think they are necessary.
>
> I am always of the opinion that pull-up resistors are a good idea.

Except on JTAG interface line nTRST.

The purpose of this line is to keep the JTAG logic in a reset state, so the
device can function normally when no JTAG driver (Wiggler, Raven, etc) is
connected. Only when a JTAG driver is connected and using the JTAG it should
drive this line high.

I found this out the hard way: if you just pullup all JTAG lines the JTAG
logic might start in a non-transparant state and the device will not start.
Connecting the nTRST line to the (hard driven) nRESET of the device with 1k
Ohm, allowing a JTAG driver to override the nTRST line, cured the problem.
This configuration even allows the use of JTAG drivers that assume a pullup
on the target and that only drive this line active low, not active high
(a.k.a. open collector).

In this system there should be pullups on TMS and TCK. Even when noise is
coupled onto thise lines they will most likely clock in '1's on TMS, which
brings the JTAG logic into RESET state after 5 TCK pulses.

Regards,
Arie de Muynck