Was this the result of some set of calculations, and, if so, on what was it based? I just picked 10K as an arbitrary value, and it seemed to work. How did you come up with that value? I've used 10 Meg, 1 Meg, 100K, 47K, 4.7K, and even 1K in various applications, with other MCU's. 10K seems innocuous enough, but there should be a rationale. I just can't find one, first, of course, because the MCU is supposed to produce 2.4 Volts on its P0 outputs when there's a load consuming 400 uA, which there isn't in this case. It should, presumably, produce a higher output voltage when the load is lower, though the old datasheet doesn't really say by how much.

This 2.4 volt level should have satisfied the HCT latches I tried in this application, but it didn't. It makes me wish I'd used 373's rather than 573's, since I've got plenty of LS373's but I'm not likely to worry about that now. If the HCT parts don't like the Voh, then there's probably some reason other than the voltage. I tried them at 8 MHz, but that didn't change anything.

What I'm wondering is whether the pullups, which don't seem to affect the CMOS part at all, are necessary in the "general" application, and, if so, exactly how one determines the desirable value.

RE