@tschak
I'm so sorry you had to write code for it.
It's funny also that shortly after the rainbow MSDOS for Phoenix, I did serial and whatever other drivers for Fido/FidoNet on the rainbow soon after.
IBM PC, rainbow, Victor 9000 were the first three. I put MSDOS on the latter two and then Fido.
(Then sanyo 555, which blocked all interrupts at every floppy access, but was by far the cheapest dos machine that could run FidoNet. Then some more foolish machines and then FOSSIL.)