> On 2018-06-10, at 11:57, André Fachat <afachat@gmx.de> wrote: > > >> What if you write to it without bit7 set? > > > > Then it doesn't change the direction. > > > > This is really a nasty behaviour, clearing the output value on direction change. > > I find it amazing what chip designers sometimes do that really annoy the programmers or users. And this sometimes even means additional hardware so it can't be attributed to scarcity of resources (like I guess clearing interrupt flags by just reading the flags....). > > My favourite is the control line of the 6551 that automatically disable receivers and/or transmitters, which makes it almost completely useless except for 3wire serial.... > > So it is not just intel that does such things... Surely not. It's just that there is something about Intel, especially of the era, that makes it less surprising ;-) -- SD! - http://e4aws.silverdr.com/Received on 2018-06-13 23:00:04
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