Intro to ACCESS.bus (RE: the ACCESS.bus Software Creator's 
	Contest Announcement)

WHAT IS ACCESS.bus?

ACCESS.bus is a new open industry standard for computer 
peripheral connectivity.  ACCESS.bus is a serial protocol that 
uses simple, low-cost I2C technology to link multiple devices to 
a single PC port.  Peripheral devices such as keyboards or 
keypads, locators (Mice, Trackballs, Joysticks), printers, VR 
gloves, digitizers, sensors, actuators or data transmitters and 
others can be easily daisy chained to the host PC.  Applications 
such as CAD/CAM, Data Acquisition, Simulation, Virtual Reality, 
Multiple-Player/Single PC Games, Education and many, many more 
can now take advantage of ACCESS.bus, the technology that puts 
Plug and Play on every PC.

The ACCESS.bus offers advantages to end-users and developers of 
systems and peripherals.  Multiple devices connect to the host 
computer with only one port.  Common communication methods for a 
number of device types lead to simplified hardware and software 
development.  As an open standard, ACCESS.bus enables cross-
platform use of the same device.

ACCESS.bus TECHNOLOGICAL DESCRIPTION:
=====================================

ACCESS.bus technology is an open specification, enabling anyone 
to implement it on host systems or in peripheral devices without 
fee or royalty.
ACCESS.bus has a bus topology architecture.  That is, a single 
host can accommodate up to 125 peripheral devices.  ACCESS.bus 
data rate is 100 Kbits/sec.

ACCESS.bus Physical Layer
^^^^^^^^^^^^^^^^^^^^^^^^^
ACCESS.bus is a serial bus architecture, based on I2C hardware 
protocol, with one data line and one clock line.
Standard low-cost I2C microcontrollers handle bit-level 
handshaking, including automatic arbitration and clock 
synchronization.  

ACCESS.bus Software Protocols
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The ACCESS.bus communication protocol is composed of three 
levels: I2C Protocol, Base Protocol, and Application Protocol.

I2C PROTOCOL: This simple and efficient protocol defines 
arbitration among contending masters without losing data.  I2C 
provides for cooperative synchronization of bus partners with 
different clock rates.  Bus transactions include addressing, 
framing of bits into bytes, and byte acknowledgment by the 
receiver.  

BASE PROTOCOL: Establishes the asymmetrical interconnect between 
a host computer and multiple peripherals.  The host becomes the 
ACCESS.bus manager.  The Base Protocol defines the format of an 
ACCESS.bus message envelope, which is an I2C bus transaction with 
additional semantics, including checksum.
Unique features of the Base Protocol are auto-addressing and hot 
plugging.  Auto-addressing assigns devices with unique bus 
addresses, without the need for setting jumpers or switches.  Hot 
plugging is the ability to attach and detach devices while the 
system is running, without rebooting.

APPLICATION PROTOCOL: This is the highest level of the ACCESS.bus 
protocol which defines message semantics specific to particular 
types of devices.  Each type requires a different Application 
Protocol.  Three broad device types have been identified: 
keyboards, locators, and text devices.

ACCESS.bus support on the PC
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
All three levels of the ACCESS.bus protocol are supported on the 
PC.  An add-on card implements the physical layer and uses the 
base protocol to communicate with physical ACCESS.bus devices.  
An ACCESS.bus Manager - TSR under DOS and a DLL under Windows 3.1 
- controls the operation of the physical layer and interacts with 
the ACCESS.bus device drivers.  Drivers are available for 
multiple ACCESS.bus keyboards, locators and printers for DOS and 
Windows 3.1.  Also available are C language source code examples 
of the interface from applications to the device drivers.


To Contact ABIG (the ACCESS.bus Industry Group):