I wrote code for a PC and an embedded system to use modems -- relatively simple stuff like dial up, hang up, wait for a call, set baud rate. Nothing fancy. We

I wrote code for a PC and an embedded system to use modems -- relatively simple stuff like dial up, hang up, wait for a call, set baud rate. Nothing fancy. We tested about 10 different modems. All of them had their own unique bugs I had to work around. Or maybe one of them didn't have any bugs (that I ran into) -- it's been thirty years.