After more testing, it seems there is no real need for the 18.432Mhz crystals. Since they cost money (a buck) and require two pins, I’ve decided they are not worth the trouble so I’ll be disabling them on my test widgets. In the meantime, I’ve tweaked the s/w uart (which is how this all started) and made it work really solid using the standard on chip clock. If you would like the source, it’s adapted from a project I got off of AVRFreaks. This only offers transmit, no receive, I use it primarily for driving two mp3 sound cards but it’s also useful for debugging. You can find the source here: