CDB5378 datasheet(29/72 Pages) CIRRUS

29 / 72 page

CDB5378

DS639DB3

2.3.5.2

I2C - SCL, SDA, Bypass

The I2C telemetry connections to CDB5378 transmit and receive through RS-485 twisted pairs. Because

signals passing through the transceivers are actively buffered, full I2C bus arbitration and error detection

cannot be used (i.e. high-impedance NACK).

The I2C inputs and outputs can be externally wired to create either a daisy chain or a bus-type network,

depending how the telemetry system is to be implemented. Analog switches included on CDB5378 can

bypass the I2C signals to create a bus network from a daisy chain network following address assignment.

When CDB5378 is used in a distributed measurement network, each node must have a unique address.

This address is used to transmit individual configuration commands and tag the source of returned con-

version data. Address assignment can be either dynamic or static, depending how the telemetry system

is to be implemented.

Dynamic address assignment uses daisy-chained I2C connections to assign an address to each mea-

surement node. Once a node receives an address, it enables the I2C bypass switches to the next node

so it can be assigned an address.

Static address assignment has a serial number assigned to each node during manufacturing. When

placed in the network, the location is recorded and a master list of serial numbers vs. location is main-

tained. Alternately, a location-dependent serial number can be assigned during installation.

2.3.6

UART Connection

A UART connection on CDB5378 provides a low-speed standardized connection for telemetry solutions

not using I2C. UART connections are provided for custom programming convenience only and are not

directly supported by the CDB5378 PC evaluation software or microcontroller firmware.

Specification

Value

I2C Inputs, 2 wires each

SCL±, SDA±

I2C Outputs, 2 wires each

BYP_SCL±, BYP_SDA±

I2C Bypass Switch Control

BYP_EN

Specification

Value

UART Connections, 2 wires each

TX/GND, RX/GND

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