user34345: Link to pin description and to the Datasheet.
I'm thinking about connecting channel outputs to LEDs and control the clock with IO-Arduino or a 555: I would program it with a 595 register.
Can someone explain me why this is a bad idea?

user4143: I wouldn't say it was a "bad" idea - pointless maybe, but not "bad". A good learning experience if nothing else.

34345: <p><a href="http://www.z80.info/z80ctc.htm" rel="nofollow noreferrer">Link to pin description</a> and <a href="http://www.google.com" rel="nofollow noreferrer">to the Datasheet</a>.</p>

<p>I'm thinking about connecting channel outputs to LEDs and control the clock with IO-Arduino or a 555: I would program it with a 595 register.</p>

<p>Can someone explain me why this is a bad idea?</p>
 4143: <p>I wouldn't say it was a "bad" idea - pointless maybe, but not "bad". A good learning experience if nothing else.</p>
