jhs@MITRE-BEDFORD.ARPA (09/10/88)
Based on my (limited) experience, you may find the problem has to do with something as simple as the polarity of the strobe put out by the computer being wrong for the latch you are using. You need to understand the timing of the data on the bus and the strobe signal your latch is responding to. When you get it all figured out, a few nanoseconds shouldn't be critical; but things like the polarity of the strobe or the edge you sample on ARE critical. In general, you should never rely too much on the time delay along a signal path relative to another path (e.g. the strobe). Instead, you should derive signals in such a way that they HAVE to have the right timing sequence. (Sangster's First Law of Logic Design: If you want signal B to happen later than Event A, DERIVE signal B from Event A.) Are you reading data directly off the parallel bus, e.g. on an 800XL, or are you using the joystick ports as an output? In either case, give me a little more detail on your interface and I might be able to help. -John Sangster / jhs@mitre-bedford.arpa