Lpc2000

>From: Soeren Gust <gust@...>
>Reply-To: lpc2100@yahoogroups.com
>To: lpc2100@yahoogroups.com
>Subject: Re: [lpc2100] JTAG interface
>Date: Mon, 2 Feb 2004 14:57:53 +0100
>
>On Sun, Feb 01, 2004 at 06:15:29PM -0000, leon_heller wrote:
> > I've just traced through the circuit of the Wiggler, simplified it (I
> > didn't see why it needed two buffers in series on most of the signals)
> > and put it into my PCB package as a schematic. I've uploaded it as a
> > PDF file, if anyone cares to check it.
>
>Don't you have to put the resistors between the parallel port and the
>buffer? The buffer gets its power from the target board which is 3.3V.
>As far as I know PC parallel ports are still running at 5V, at least
>older ones. The AC244 does have the usual input protection diodes, so
>I think you need current limiting resistors between PC and buffer.
>
>Or is there some kind of magic going on which I don't understand?


Yes, it probably would be a good idea. The Wiggler doesn't have them, 
though. I'm actually using an HC244 - it works OK. The  parallel port I'm 
using has resistors in series with the outputs, anyway. I think the 
resistors on the JTAG outputs are to stop ringing on the lines.

Leon
--
Leon Heller, G1HSM Tel: +44 1424 423947
Email: aqzf13 at dsl dot pipex dot com
WWW: http://www.geocities.com/leon_heller

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