PS/2 Interface (was: Wang 300 Calc]

How about the Facit 4070 paper tape punch? It has a DB25 connector on the rear panel. Inside there are 2 slots. One takes the control logic/driver PCB for the punch. The parallel input of that is wired to one side of the other eddge connecotr ; the other side of that connecotr is wired to the DB25. Most of the time theres a 'jumoper board' in that second slot, bringing the parallel interface (TTL levels, close to Centronics but not quite) on the DB25 connector. But you could also get a serial interface PCB, really a a serial-parallel converter. This pluggeed in place of the jumper board and gave an RS232 interface (normal pinouts, but with a current loop on a couple of the normally spare pins) on said DB25. So with that unit the only way to tell whether that DB25 is an RS232 serial interfxce or a TTL level parallel interface is to look at what PCB is fitted. -tony