A four-wire (TX, RX, RTS, CTS) RS-232 interface is provided via a 10-pin 0.1" boxed header. These headers are used on old ISA Serial Port expansion cards for when the 9-pin D-Sub (DE9, not DB9) receptacle didn't fit on the edge of the card and had to be moved to a second bracket, one slot over.

The DTR, DSR, DCD and RI pins are not connected.