The Access.bus was developed in the early 1990s by over 60 well-known companies. It is an I/O bus for connecting peripheral devices directly to a computer, comparable to the Universal Serial Bus( USB) or FireWire. Although the Access.bus was developed before the USB interface, it did not find sufficient support in the industry.
The bidirectional Access.bus defines the physical layer, the transmission media and the connectors, whereas the protocol layers correspond to those of the I2C bus. In contrast to the latter, the Access.bus is a 4- wire bus, with two lines used for the positive supply voltage and ground, and the other two for the clock and data signals. In terms of addressing, it corresponds to the standard version of I2C with an addressing range of 7 bits, corresponding to 125 devices, and in its data transfer rate to the slow transfer rates of I2C with 10 kbit/s and 100 kbit/s over up to 10 m.
The Access.bus supports external peripherals such as displays, keyboards, mice, joysticks, etc. as well as intelligent internal units such as graphics boards, video boards, power supplies and power management components. Since the intelligent devices share the same system interface, the system management functions and for communication with the peripherals can be made more effective and requires fewer interrupt lines and I/O addresses. The Access.bus specifications are developed and published by the Access.bus Industry Group (ABIG).