Pin Assignment for the Serial Port (RS-232C)

1.  N/C
2.  Transmit Data
3.  Receive Data
4.  RTS (Request To Send)
5.  CTS (Clear To Send)
6.  DSR (Data Set Ready)
7.  Signal Ground
8.  CD (Carrier Detect)
9.  +Transmit Current Loop Return (20ma)
10. N/C
11. -Transmit Current Loop Data (20ma)
12. N/C
13. N/C
14. N/C
15. N/C
16. N/C
17. N/C
18. +Receive Current Loop Data (20ma)
19. N/C
20. DTR (Data Terminal Ready)
21. N/C
22. RI (Ring Indicator)
23. N/C
24. N/C
25. -Receive Current Loop Return (20ma)