ACCESS.bus (A.b)

Last Updated: August 18, 2011

Definition - What does ACCESS.bus (A.b) mean?

ACCESS.bus (A.b.) is a serial bus that interconnects slower peripheral devices to a motherboard, mobile phone or embedded system. It is designed as an interface for slow-speed devices such as a mouse or keyboard. Its structure is similar to a USB but it has a smaller bandwidth.

ACCESS.bus was first developed in 1985 by Philips Semiconductors and the Digital Equipment Corporation and is defined by Philips' inter-integrated circuit (I²C) bus standards.

Phillips' objective for the A.b was to outline a single standard to be used for internal and external devices. The I²C/A.b controller would be used internally for internal devices while the external A.b connector permitted peripheral devices to be connected to the bus. This design allowed all slow and medium-speed devices to operate under one controller and protocol suite.

Unfortunately, the A.b never caught on with the majority of consumers. Today, the A.b is still available but is seldom used because it was replaced by the much faster USB.

Techopedia explains ACCESS.bus (A.b)

ACCESS.bus was developed for easy installation and configuration, using a bus topology that supports up to 125 devices. Although it was superseded by the USB, it is still a standard interface for a monitor to configure setup information to a host graphics card.

With the same I²C protocol, the A.b supports a bidirectional, two-wire serial bus with the following features:

Hot swappable
Backward compatible
Supports seven-bit and 10-bit addresses
Low-speed analog-to-digital and digital-to-analog controllers
Master and/or slave devices can coexist on the same bus depending on the mode

Compared to a USB, one of the main advantages of an A.b is that it can be both a slave and a master. A USB can only be a slave. Since the A.b can be a master or slave it can connect several devices together without a host PC.

Another advantage of ACCESS.bus is that it can connect several devices together to make one daisy chain instead of requiring a massive cable. It can also support a hub. The disadvantage is that it has a slower data transfer rate than the USB.