Lpc2000

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Leon Heller wrote:
> ----- Original Message -----
> From: "sixtyfivebit" <sixtyfivebit@...>
>> I'm glad this thread is helping other people, and after some research
>> things are a bit more clear...
>>
>> Since I really don't want to buy a wiggler and would rather build one
>> my self (for experience, learning, etc.), is there any particular
>> schematic I should go with?
>>
>> Leon_Heller, nice site and I saw your prototype page earlier
>> (bookmarked it), but I couldn't find your jtag.zip. I went through
>> most of the pages on your site but didn't see it... did I miss something?
> 
> It's in this groups Files area.

Hi Leon,

Sorry if I'm asking a stupid question (I'm not a hardware designer),
but is your circuit safe for the parallel port?

As far as I can see the 74HC244 takes its VCC from the 3.3V from
the target board while the 5V parallel port signals are directly
connected to the inputs of the HC244. In the HC244 datasheet I
notice that there are protection diodes between the inputs and
Vcc / ground.

It looks like there is a current path from the 5V parallel ports pins
through the HC244 protection diodes into the target 3.3V without any
obvious current limit. Doesn't this risk blowing out the parallel port
drivers? Also, wouldn't this lift the 3.3V on the target to a possibly
dangerous voltage?

Regards,
Bertrik
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