RS232 interface for 68HC11

The Motorola 68HC11 microcontroller is packed with features and consequently requires very few parts to make a minimum system configuration. In principle, such a system does not need an RS232 interface because that is usually only necessary to be able to load programs into the controller’s on-chip EEPROM memory. For the actual use of the program, the interface is not required. The RS232 interface described here is therefore built on a separate little board, and may be used at any time for programming and troubleshooting 68HC11 controller applications.