Cirrus Logic CRD5376 - Manual (Page 27)

CRD5376
DS612RD2 27
2.3.4.1 CLK, SYNC
Clock and synchronization telemetry signals into CRD5376 are received through RS-485 twisted pairs.
These signals are required to be distributed through the external system with minimal jitter and timing
skew, and so are normally driven through high-speed bus connections.
Synchronization of the measurement channel is critical to ensure simultaneous analog sampling across
a network. Several options are available for connecting a SYNC signal through the RS-485 telemetry to
the digital filter.
A direct connection is made when the SYNC_IO signal is received over the dedicated RS-485 twisted pair
and sent directly to the digital filter SYNC pin through jumper R93. The incoming SYNC_IO signal must
be synchronized to the network at the transmitter since no local timing adjustment is available.
A microcontroller hardware connection is made when the SYNC_IO signal is received over the dedicated
RS-485 twisted pair and detected by a microcontroller interrupt. The microcontroller can then use an in-
ternal counter to re-time the SYNC signal output to the digital filter SYNC input as required.
A microcontroller software connection is made when the SYNC signal output is created by the microcon-
troller on command from the system telemetry. The microcontroller can use an internal counter to re-time
the SYNC signal output to the digital filter SYNC input as required.
2.3.4.2 I2C - SCL, SDA, Bypass
The I2C telemetry connections to CRD5376 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 CRD5376 can
bypass the I2C signals to create a bus network from a daisy chain network following address assignment.
When CRD5376 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-
Specification Value
Synchronous Inputs, 2 wires each
CLK±, SYNC±
Specification Value
Distributed SYNC Signal Synchronization
± 240 ns
Distributed Clock Synchronization ± 240 ns
Analog Sampling Synchronization Accuracy ± 480 ns
Specification Value
I2C Inputs, 2 wires each
SCL±, SDA±
I2C Outputs, 2 wires each BYP_SCL±, BYP_SDA±
I2C Bypass Switch Control BYP_EN