I2C Bus Description and Pinout

I²C Bus / Access Bus

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I²C Bus Description

I²C bus [Inter-IC Bus] or [IIC Bus] was originally designed to be a battery control interface. The I²C bus uses a bi-directional Serial Clock Line [SCL] and Serial Data Lines [SDA]. Both lines are pulled high via a resistor [Rp]. Resistor Rs is optional, and used for ESD protection for 'Hot-Swap' devices. No other lines are specified. Three speed modes are specified: Standard; 100kbps [Bits per Second], Fast mode; 400kbps, High speed mode 3.4Mbps. I2C, due to its two-wire nature (one clock, one data) can only communicate half-duplex. The maximum bus capacitance is 400pF, which sets the maximum number of devices on the bus and the maximum line length. The interface uses 8 bit long bytes, MSB [Most Significant Bit] first, with each device having a unique address. Any device may be a Transmitter or Receiver, and a Master or Slave. Data and clock are sent from the Master ~ valid while the clock line is high. The link may have multiple Masters and Slaves on the bus, but only one Master may be active at any one time. Slaves may receive or transmit data to the master. I²C defines the electrical layer and protocol, and was developed by Philips Semiconductors. V_DD may be different for each device, but all devices have to relate their output levels to the voltage produced by the pull-up resistors [R_P].

Access Bus Description

Access.Bus is a low speed serial bus aimed at the PC (serial bus) market. Access.Bus uses the I²C bus as the electrical hardware interface. A four pin modular type connector and a shielded 4 wire cable is called out in the specification. ACCESS.bus operates at 100 Kbps with a maximum cable length is 10 meters, however a repeater may be added to increase the bus length. Access.Bus uses the same signals as the I²C bus, and adds ground and power, pin out below. The specification is controlled by the ACCESS.bus Industry Group (ABIG).

Access.Bus Pinout
Pin 1: GND, Black(#26AWG) [AWG: American Wire Gage]
Pin 2: SDA [Send Data], Green (#28AWG)
Pin 3: +5v, Red (#26AWG)
Pin 4: SCL [Serial Clock], White (#28AWG)
Shield: Connected only to the host connector shield and host ground

The Access.Bus specification [see below] also calls out pull-up and serial resistors located on the host.

{AccessBus and I2C Bus Index}

I2C Bus Interface IC Manufacturers

Hendon Semiconductor {2-wire bi-directional Bus Buffer}

Maxim {12-Bit Plus Sign Temperature Sensors with SMBus/I2C-Compatible Serial Interface}

NXP {I²C Bus}

Many ICs have the I2C interface including some processors and controllers.

IC Chip Manufacturers {All other types} {This web Site}

{AccessBus and I2C Bus Index}

I2C and AccessBus Standards Info

The I2C-Bus Specification Version 2.1 Jan. 2000
The I2C standard was released by Philips, which is now NXP

AccessBus Protocol Specification{Micro Computer Control Corp.}

{Back to AccessBus and I2C Bus Index}

Engineering Design Key words: AccessBus, Access.Bus, Access Bus, I2C Bus, IIC Bus, Inter-IC Bus Standard, Interface Standard, Specification, Spec, Interface, IC, Serial Bus, Battery Control Bus, Physical Interface, Description, Personal Computer Interface, PC, Peripheral Interface, Chip-to-Chip.


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Last Modified 12/19/08

I2C Bus / Access Bus