I'm just writing the SW for emulating the parallel printer interface, have to exchange one parallel printer with serial one. It's pretty trivial, as FoxyRick wrote. besides data, only two handshake lines BUSY and STROBE.
It goes like this:
1) upon receiving valid data from the system that wants to print, on asserted STROBE signal, assert BUSY to the printing system
2) send received data serially to the printer
3) after data is sent deassert BUSY signal
4) GoTo 1) :-D