Manual

CRD5378

DS639RD2 25

Telemetry signals enter CRD5378 through RS-485 transceivers, which are differential current mode

transceivers that can reliably drive long distance communication. Data passes through the RS-485 trans-

ceivers to the microcontroller I

C interface and the clock and synchronization inputs.

2.3.3.1 CLK, SYNC

Clock and synchronization telemetry signals into CRD5378 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 (with a 0 Ω resistor installed at R71). 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.

Specification Value

RS-485 Transceiver - Linear Tech LTC1480IS8

Surface Mount Package Type SOIC-8, 5mm x 6mm

Supply Voltage, Quiescent Current

3.3V, 600 µA

Maximum Data Rate 2.5 Mbps

Transmitter Delay, Receiver Delay 25 - 80 ns, 30 - 200 ns

Transmitter Current, Full Termination (60 Ω)

25 mA

Transmitter Current, Half Termination (120 Ω)

13 mA

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