UART Device

Typical Serial and Parallel Ports of 20th Century

The RS-232 serial port was widely used in the 20th century for character I/O devices (teletype, printer, dumb terminal).

A pair of simplex channels (output and input) make it full duplex.

Additional wires are sometimes used for hardware flow control, or a software Xon/Xoff protcol can be used.

Baud rate and number of bits per words must be pre-agreed.

Serial Port Connector (9 pin instead of original 25 pin).

Teletype/teleprinter: These devices were almost entirely mechanical with the electric circuit being little more than one switch activated by cams for transmit and one solenoid for receive.