SBus - Chip and Module Interconnect Bus

1. Scope and object

SBus is a high performance computer I/O interface for connecting integrated circuits and SBus Cards to a computer system motherboard. This standard defines the mechanical, electrical, environmental, and protocol requirements for the design of SBus Cards and the computer system motherboard that supports those cards. Every SBus Card shall implement appropriate self-descriptive and initialization firmware using FCode, which is similar to the Forth programming language. The details of this firmware standard are beyond the scope of this standard.1) In addition, other software interfaces may be used for communication with SBus Cards.

SBus is intended to provide a high performance I/O bus interface with a small mechanical form factor. The small size, high levels of integration, and low power usage of SBus Cards enable them to be used in laptop computers, compact desktop computers, and other applications requiring similar characteristics. SBus Cards are mounted in a plane parallel to the motherboard of the computer system, allowing the computer system to have a low profile.

SBus is not designed as a general purpose backplane bus. SBus allows transfers to be in units of 8, 16, 32, or 64 bits. Burst transfers are allowed to further improve performance. SBus allows a number of SBus Master devices to arbitrate for access to the bus. The chosen SBus Master provides a 32-bit virtual address which the SBus Controller maps to the selection of the proper SBus Slave and the development of the 28-bit physical address for that Slave. The selected SBus Slave then performs the data transfers requested by the SBus Master. Simple SBus Cards may be designed to operate solely as Slaves on the SBus.