Figure 3—There are two regulators, one for 5 V to run the LCD and another for 3.3 V to run the microcomputer. An optically isolated interface to the Icom CIV programming bus is used to reduce receiver noise caused by ground loops. The ubiquitous MAX232 is used to interface to the PC serial ports. (The data line currently isn’t used.) The microcomputer can be programmed with Zilog software by connecting the debug line to a serial port on your PC.