Jeffrey Golas says, he's having problems running a UART echo program on his MITS Altair. He says he's doing this and that, entering this program and code and that, and getting results or not which he doesn't understand. Well, Jeffrey Golas: you are doing the right sort of things! You are trying to understand the codes, and understand the hardware you have. You are testing one thing or another thing, and looking at results, and trying to decide "what's next? what works? what doesn't work?" That is correct. This is what one did with MITS Altairs in the era. They learned how to use them, at the binary level - like you are. They learned how the hardware worked, chip by chip, signal by signal. Why would that change NOW - if the hardware is the same, the software and front panel are the same? So: now that you have some experience and are at the limits of what you know: it's time to do some homework, to stretch your limits. Sorry, but this is actually the fun part. Re-read those MITS manuals now, and the Intel 8080 manual, and the UART manual. Learn more about how the front-panel works, and how the 8080 and the UART (whatever board it is) works. Try other UART programs, simpler ones. Use some test equipment, to see the signals on the boards! Then, toggle in more code. Check the wiring and settings on that UART board. Go where the symptoms lead you. This is the fun part! And if this isn't fun, why the hell have an Altair around? That's your call of course, but you have my opinion on the matter. I think you are doing fine. Just keep doing it. Regards, Herb Johnson -- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net preserve, recover, restore 1970's computing email: hjohnson AT retrotechnology DOT com or try later herbjohnson AT retrotechnology DOT info