IІC (Inter-Integrated Circuit; I2C or IIC) is a synchronous, multi-master/multi-slave (controller/target), packet switched, single-ended, serial communication bus invented in 1982 by Philips Semiconductors. It is widely used for attaching lower-speed peripheral ICs to processors and microcontrollers in short-distance, intra-board communication.
Several competitors, such as Siemens, NEC, Texas Instruments, STMicroelectronics, Motorola, Nordic Semiconductor and Intersil, have introduced compatible IІC products to the market since the mid-1990s.
System Management Bus (SMBus), defined by Intel in 1995, is a subset of IІC, defining a stricter usage. One purpose of SMBus is to promote robustness and interoperability. Accordingly, modern IІC systems incorporate some policies and rules from SMBus, sometimes supporting both IІC and SMBus, requiring only minimal reconfiguration either by commanding or output pin use.