The P82B96 device is a bus buffer that supports bidirectional data transfer between an
I2C bus and a range of other bus configurations with different voltage
and current levels.
One of the advantages of the P82B96 is that it supports longer cables/traces and allows
for more devices per I2C bus because it can isolate bus capacitance such
that the total loading (devices and trace lengths) of the new bus or remote
I2C nodes are not apparent to other I2C buses
(or nodes). The restrictions on the number of I2C devices in a system
due to capacitance, or the physical separation between them, are greatly improved.
The device is able to provide galvanic isolation (optocoupling) or use balanced
transmission lines (twisted pairs), because separate directional Tx and Rx signals are provided.
The Tx and Rx signals may be connected directly (without causing bus latching), to provide an
bidirectional signal line with I2C properties (open-drain driver).
Likewise, the Ty and Ry signals may also be connected together to provide an bidirectional signal
line with I2C properties (open-drain driver). This allows for a simple
communication design, saving design time and costs.
Two or more Sx or Sy I/Os must not be connected to each other on the same node. The
P82B96 design does not support this configuration. Bidirectional I2C
signals do not have a direction control pin so, instead, slightly different logic low-voltage
levels are used at Sx/Sy to avoid latching of this buffer. A standard
I2C low applied at the Rx/Ry of a P82B96 is propagated to Sx/Sy as a
buffered low with a slightly higher voltage level. If this special buffered low is applied to the
Sx/Sy of another P82B96, the second P82B96 does not recognize it as a standard
I2C bus low and does not propagate it to its Tx/Ty output. The Sx/Sy
side of P82B96 may not be connected to similar buffers that rely on special logic thresholds for
The Sx/Sy side of the P82B96 is intended for I2C logic voltage
levels of I2C master and slave devices or Tx/Rx signals of a second
P82B96, if required. If Rx and Tx are connected, Sx can function as either the SDA or SCL line.
Similarly, if Ry and Ty are connected, Sy can function as either the SDA or SCL line. There are no
restrictions on the interconnection of the Tx/Rx and Ty/Ry I/O pins to other P82B96s, for example
in a star or multi-point configuration (multiple P82B96 devices share the same Tx/Rx and Ty/Ry
nodes) with the Tx/Rx and Ty/Ry I/O pins on the common bus, and the Sx/Sy side connected to the
line-card slave devices.
In any design, the Sx pins of different devices should never be linked, because the
resulting system would be very susceptible to induced noise and would not support all
I2C operating modes.
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