Photos of a Northstar Computer S100 motherboard.
There are two serial ports, bootstrap rom and options, and a parallel in and out port on the rear of the motherboard, along with regulation for that logic, and for the +5 +12 for the floppy drives in the system.
Link is for Horizon system, but includes motherboard schematic.
http://bitsavers.org/pdf/northstar/ns_hrzd.pdf
