Hi all,
  I'm asking if there is any difference between the Xilinx JTAG III
and IV??? I saw that the speed of the second is 8 time quicker than
the first, but i need a JTAG cable and all the schematics are for the
old one. Is it matter if i use the JTAG III instead of the PC4???
  thanks

"jack lalo" <j...@hotmail.com> schrieb im Newsbeitrag
news:a...@posting.google.com...
> Hi all,
>   I'm asking if there is any difference between the Xilinx JTAG III
> and IV??? I saw that the speed of the second is 8 time quicker than
> the first, but i need a JTAG cable and all the schematics are for the
> old one. Is it matter if i use the JTAG III instead of the PC4???
>   thanks

The good old one is just a tristate buffer. Can be easy rebuild. But you
should add a RC-filter and two schmitt triggers in from of the TCK/CCLK
line, since the signal from the parallel port might by noisy. Another point
is, that the PC-III is only recommended with IO voltages of 5/3.3V. 2.5
might work or not. PC-IV works down to 1.5, AFAIK. And its faster, since it
uses (years too late) ECP mode to transfer 8 bit of data and serialize them
on the POD. Some yaers ago I did my own download cable design, using a 32
macrocell coolrunner and own control software. Downloading was at an
instant. BING!! Why the hell has noone already done something like this and
sells them? Especially for the big Virtex-II'n stuff life would be so much
easier.

Regards
Falk

P.S. I can email you the modified schematics of the PC-III if you like. Drop
me a mail.