I found this interesting interface on the main Siemens S5-95U device (for automation systems, introduced in 1979). Often, you see the interface in the middle missing. Not sure how this bus is called. You put single wires into the 2 rows in the middle. 16 digital input and 16 output, but there are 20 holes each. 4 might be alarm/counter inputs. Analog i/o is on the right. Optional L1/L2 PROFIBUS.
