Have you considered (not sure about the full requirements) but designing a secondary expansion board with serial controllers instead of the expansion headers?? Just an idea, but the Motorola version of the serial processor (6850?) should be a good (...) (26 years ago, 11-Mar-99, to lugnet.robotics.handyboard)
I have considered something like that and it sure would work but I was hoping to find a s/w based solution that didn't require changing the h/w. I only need outputs, 2400bps, and I dont need any of the more functional aspects of typical serial parts (...) (26 years ago, 11-Mar-99, to lugnet.robotics.handyboard)