It doesn't take a rocket scientist to figure that out, Erik. There are modes of communication other than ASYNC, and most of them are more efficient. That's WHY they exist. ASYNC mode is useful when you have communication of a generic nature, low rate (read the RS232 standard and see how you're violating its rate limitations! Almost everyone does ... ), short distance, high error tolerance. If you have to communicate over a long distance, with large data volume at a high rate, ASYNC should be your absolute last choice. Of course, it will still work, but the reason for its popularity is its inherent 5% rate error tolerance. Since it resets after every character, it is inherently tolerant.

The serial port of the 805x was undoubtedly designed by the boss' nephew or son-in-law, hence was never criticized for the fact that it screwed up the entire device because of its dependence, not only on the timer used as its baud rate generator but also because of its inherent imposition of a limited range of MCU oscillator frequencies. The guy and his boss should have been taken out and shot, then sold for spare parts. Had modern transplant technology existed in the late '70's, they probably would have done that.

Now, I don't promote the use of Mode-0 where it won't work. There are devices other than PC's in the world though, and you should recognize that they don't all "talk" ASYNC protocol.

I recognize that the Mode-0 port is essentially useless on a 12-clocker, and even on a 6-clocker, at least in the context of synchronous comm's or sampling. The 4-clockers and those faster, particularly the one-clockers from Maxim/Dallas, which are of some interest to me, can make use of Mode-0, though they haven't published nearly enough detail about how their serial port works in Mode-0. I'll be looking at it in considerable detail, but not this week. Of course, I can only guess at what's going on inside, but I do have a logic analyzer and oscilloscope. When I have something definitive, I'll share it with this forum if it looks to be of use.

There's no guarantee, BTW, that this mfg or that will have a serial port that works EXACTLY like the original Intel model, particularly in Mode-0, since it's considered rather esoteric. When I last spoke with the guy who's handling support of the DS89C4x0 series, he told me that they'd not investigate the operation of their device in Mode-0 in any detail. I'm guessing I'll see some interesting things once I put the thing under the magnifying glass.

RE