RS232

• The "serial port", an old device designed for data exchange between "nodes"
• designed for 50 feet transmission length
• designed for 19.2kb/s transmission rate
• The data flow is bidirectional, full duplex
• A serial connection has a DTE end (data terminal equipment) and DCE (data communications equipment) end. The serial socket in the PC is a DTE socket
• RS232 sockets can be 25 pin or 9 pin

Pin layout

Serial port device driver

• The h/w side of the device driver has to set voltages on the various pins
• The s/w side of the device driver has to take requests, translate them into pin settings, and return results
• A typical device is a UART 16550A

Null modem

• A serial cable can be used to connect two computers
• Since both computers have DTE sockets, the cable must "swap" some of the pin settings
• This is done by a "null modem"