CABLE DIAGRAMS FOR IBM AND SIMILAR COMPUTERS Standard RS - 232 Modem Cable DB-25 to DB-25 25 to 25 Pin Terminal (DTE) Modem (DCE) ---- ---- GND | 1 | <---------> | 1 | GND TxD | 2 |-----------> | 2 | TxD RxD | 3 | <-----------| 3 | RxD RTS | 4 |-----------> | 4 | RTS CTS | 5 | <-----------| 5 | CTS DSR | 6 | <-----------| 6 | DSR GND | 7 | <---------> | 7 | GND DCD | 8 | <-----------| 8 | DCD DTR | 20 |-----------> | 20 | DTR ---- ---- DB-9 to DB-25 9 to 25 Pin Terminal (DTE) Modem (DCE) ---- ---- TxD | 3 |-----------> | 2 | TxD RxD | 2 | <---------> | 3 | RxD RTS | 7 |-----------> | 4 | RTS CTS | 8 | <-----------| 5 | CTS DSR | 6 | <-----------| 6 | DSR GND | 5 | <---------> | 7 | GND DCD | 1 | <-----------| 8 | DCD DTR | 4 |-----------> | 20 | DTR RNG | 9 | <-----------| 22 | RNG ---- ---- CABLE DIAGRAM FOR MACINTOSH COMPUTERS RS-232 DIN 8 (MAC) Supra Modem With Hardware Handshake ----- ------ DTR HSKo | 1 |----------------> | 20 |--+ DTR CTS HSKi | 2 | <----------------| 5 | | CTS TxD TxD- | 3 |----------------> | 2 | | TxD GND GND +--| 4 | <--------------> | 7 | | GND RxD RxD- | | 5 | <----------------| 3 | | RxD N.A. TxD+ | | 6 |---nc nc---| 6 | | DSR N.A. DEAD | | 7 |---nc nc---| 8 | | DCD N.A. RxD+ +--| 8 | nc---| 1 | | GND ----- | 4 |--+ RTS ------ Note: Pins 4 & 8 are hooked together on the MAC side, and also connect to pin 7 on the Modem side. Pins 4 & 20 are hooked together on the Modem side, and also connect to pin 1 on the MAC side. Lines on DB25 port (DB9 port) Pin # Mnemonic Description 1 (NC) GND Protective frame ground 2 (3) TxD Transmit Data 3 (2) RxD Receive Data 4 (7) RTS Request to Send 5 (8) CTS Clear to Send 6 (6) DSR Data Set Ready 7 (5) GND Reference signal ground 8 (1) DCD Data Carrier Detect 20 (4) DTR Data Terminal Ready 22 (9) RNG Ring Indicator