Lpc2000

Randy M. Dumse wrote:

> The 20 pin JTAG connector is quite a waste of pins. There's only
> a few active signals on the connector. A 20 pin connector would
> dominate our boards, and in some cases, require us to double
> their size. So on all our boards we have shrunk down to a 10 pin
> JTAG connector. We have adapters that go from the JTAG connector
> to the PC parallel port.

Sure, if you're just talking about a wiggler type JTAG or some sub MHz 
JTAG debugger pod that may be true.
But you will require some 'decent' cable when you go for higher 
frequencies and with JTAG speeds of 50 MHz you defenitely want a cable 
where there is shielding between the signals (and some proper cable 
impedance).
The 20 pin connector is the easiest and cheapest way to provide this. 
Another option is the use of the mictor style connectors - these are the 
fine-piched connector types you also find on logic analyzers.

So yes, for the lpc21xx controllers with JTAG speeds below 2 MHz you can 
use almost any cable you like (I just use a set of 4" long seperate 
wires to connect to my jtag port).
And yes, for faster processor cores (supporting a faster JTAG clock) you 
will need proper cabling and connectors. ARM uses a standard 20 pin 
cable on the RealView ICE but on my 200 MHz ARM system I need the 'high 
speed' cable - connection is not reliable otherwise. The board layout is 
correct and does provide proper routing of JTAG signals to the connector.

I do agree that use of the standard 100 mil header type is a waste of 
board space. There would be other connectors available that are much 
smaller in size and have even better specifications but there are some 
good things on the good-old 100 mil connectors.

Rob