Carl Fenger
Philips Semiconductors

The I²C (Inter-IC) bus has become a popular serial bus architecture which needs to be understood for proper implementation. On the hardware level, I²C is a collection of microcomputers with integrated I²C port (Philips PCD33xx, PCF84Cxxx, and many of their 80(C)51 family derivatives, plus µCs from several other manufacturers), and a peripheral set (LCD/LED drivers, RAM, ROM, E²PROM, Clock/Calendars, I/O, A/D, D/A, IR transcoders, frequency synthesizers, audio processors, telephony ICs and various tuning ICs for TV/radio). These devices all communicate serially over a two-wire bus, serial data (SDA) and serial clock (SCL). The I²C structure is optimized for hardwire simplicity. Parallel address and data buses inherent in conventional systems are replaced by a serial protocol that transmits both address and bidirectional data over a two-wire bus. This means that interconnecting wires are reduced to a minimum; only V_DD, ground, and the two-wire bus are required to link the controller(s) with the peripherals or other controllers. This results in reduced IC size, reduced pin count, and simpler interconnections. An I²C system is therefore smaller, simpler, and cheaper to implement than its parallel counterpart.