Uart

https://blog.mbedded.ninja/electronics/communication-protocols/uart-communication-protocol/

URT is a serial connection that was implemented without being standardized. UART chip 8250 and it's newer version 16450 was used as a parallel to serial interface between the processor and the slave device

RS232 was standardized in 1960 as EIA RS-232 and updated throughout the years with version TIA-232-F from 2012.

RS232 port (DE9 subcontractor / DB25) From a DTE Terminal to a DCE modem. The original 8250 had an 8 bit buffer. Tx, Rx, CTS Clear-to-Send, RTS Ready-to-Receive. RS232 has a lot of power and the voltage is between -15 and plus -15V. UART uses the voltage from the chips (e.g. 5V or 3.3V depending on the )

Tx/Rx and no clock signal. Instead stop start was used, problems with IRQ, every byte triggered an interrupt. Processor would context switch.

History

https://www.youtube.com/watch?v=2XLZ4Z8LpEE

Teletype on a 20mA current loop