Here are the RS-232 (DB-25) equivalent pinouts for the IBM PC/AT (DB-9) serial connector:
IBM PC/AT DB-25 (DTE)
DB-9 equivalent
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1 8 (CD)
2 3 (RXD)
3 2 (TXD)
4 20 (DTR)
5 7 (SG)
6 6 (DSR)
7 4 (RTS)
8 5 (CTS)
9 22 (RI)
Reference
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RS-232 Signal (DB-25)
1 - Sig Gnd: Normally Shield or Chassis Ground
2 - TXD: Transmit Data
3 - RXD: Receive Data
4 - RTS: Request to Send
5 - CTS: Clear to Send
6 - DSR: Data Set Ready
7 - GND: SIGNAL Ground
8 - DCD: Data Carrier Detect
20 - DTR: Data Terminal Ready
22 - RI: Ring Indicate