Originally Posted by Ami_GFX
I own one of the ST multiport adapters, the Unitor N. It plugs into ST's cartridge port which is much faster than an RS232 serial port. It brings the total number of MIDI ports to 6 on the ST. It also adds SMPTE so the sequencer can be synced to a tape recorder. Steinberg produced a similar device. There were many such devices for the Mac and I have an old one for the PC as well that uses the parallel port and adds two MIDI ports that can be used alongside the joystick midi port on the PC.
As i wrote - additional module, additional extension, additional circuitry but not multiport solution based on Atari ST embedded MIDI (i.e. single UART - MC6850 ACIA) - i never wrote that this is not possible - same rule can apply for any computer also Amiga - with additional hardware many independent MIDI ports can be created.