When building circuits, many peripherals accept data via a serial, RS232-style connection. Cheap micro controllers(e.g. PIC16F84A) don’t have an internal UART though…”bit banging” a port is due.
Dallas Maxim has published an application note on how to implement a software UART on one of its MAX controllers; but the information is also useful for most other controller types.
I needed sth like this a few weeks ago…enjoy: