2.3.3 Serial Cables - Notes
Serial / RS-232
- Transmits data one bit at a time over a single wire
- Uses start, stop, and parity bits to format and verify data
- Maximum speed is about 115 Kbps, much slower than modern interfaces
- Originally used for dial-up modems
- Still found on some network equipment for device management
- In Windows, it appears as a COM port
The Connector
RS-232 technically specifies a 25-pin connector, but most PCs used the cheaper 9-pin DB9 connector instead. This is a D-subminiature connector, and the PC port is typically female.
PS/2 (Bonus Legacy Port)
- Used for mice and keyboards
- 6-pin mini-DIN connector
- Color coded: green for mouse and purple for keyboard
Quick Recap of Legacy Ports
| Port | Pins | Signal | Still used? |
|---|---|---|---|
| VGA | 15 | Analog video | Mostly phased out |
| DB9 Serial | 9 | Data (RS-232) | Rare / niche |
| PS/2 | 6 | Mouse/keyboard | Very rare |
Key Things to Remember
- Serial communication sends data one bit at a time.
- RS-232 is a legacy standard and is much slower than modern interfaces.
- Most PCs used a 9-pin DB9 connector instead of the original 25-pin form.
- PS/2 is another legacy connector used for keyboards and mice.