RS232 (COM port)

This is RS232 (COM) port, in electronics COM ports are called RS232. This picture is RS232 9 pin female connector and Pin assignments.
Usually use pin 2, 3 and 5. Pin-2 is for transmit low byte (4 bit) data. Pin-3 is for receive low byte (4 bit) data. Pin-5 is for ground. So you can send only 16 channels for using that 3 pins. You can use normally up to 255 channel by using Pin-7 and 8 for next 4-bit high byte, combination all 8-bit (Low+High) channels.