Lpc2000

--- In lpc2000@yahoogroups.com, "Ed Schlunder" <zilym@y...> wrote:
>
> Thank you for all the suggestions. I have put together an initial
> schematic diagram using 74VHC14 schmitt trigger inverters and RC low
> pass filters (as suggested here):
> 
> http://www.k9spud.com/jtag/
> 
> I'm not sure how to add additional signals like RTCK and nTRST. Won't
> these kind of changes require software support on the PC to be useful?
> My understanding was that the Macraigor software was not open source.
> Where should these signals be connected to on the PC side?
> 
> Or are you just suggesting a jumper for the user to manually switch by
> hand?
> 
> What is the nTRST signal useful for? I'm new to JTAG, just trying to
> get my first ARM project started.
> 

Ed, your use of 'HC14 parts is exactly the same as ARM did in their
Application Note 31.  IMHO, I think that you will find the RC time
constant of your filters to be much too long!  With such large
resistors, the input capacitance of the of the Schmitt triggers will
probably be plenty of low pass filtering!  Also, if you want to save a
few parts, you can replace the transistor inverter and it's assocoated
base resistors with one of your left over 'HC14s with a series diode
on it's output to convert it to an equivalent of an open drain output.

A1. The signal connections on the PC side are fixed by the closed
source Macraigor software, so added enhancements to the hardeware will
not have Macraigor software support. In any case, the Wiggler clock is
probably much too slow for RTCK to be very useful unless the target
ARM is being clocked at a much slower than normal speed. RTCK has been
VERY useful for very high speed JTAG debuggers like TRACE32.

A2. The nTRST signal is the JTAG TAP controller reset. The other reset
signal is for the rest of the hardware. In other words, ARM intended
for them to be separately resetable, as they explain in section 12.3
of Application Note 31.

Regards,
-- Dave