Cirrus Logic CRD5378 - Manual (Page 26)

CRD5378
26 DS639RD2
2.3.3.2 I
2
C - SCL, SDA, Bypass
The I
2
C
®
telemetry connections to CRD5378 transmit and receive through RS-485 twisted pairs. Because
signals passing through the transceivers are actively buffered, full I
2
C bus arbitration and error detection
cannot be used (i.e. high-impedance NACK).
The I
2
C 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 CRD5378 can
bypass the I
2
C signals to create a bus network from a daisy chain network following address assignment.
When CRD5378 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 I
2
C connections to assign an address to each mea-
surement node. Once a node receives an address, it enables the I
2
C 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.
2.3.4 UART Connection
A UART connection on CRD5378 provides a low-speed standardized connection for telemetry solutions
not using I
2
C. UART connections are provided for custom programming convenience only and are not di-
rectly supported by the CRD5378 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