CDB5376 Datasheet, PDF (29/78 Pages) Cirrus Logic – Multichannel Seismic Evaluation System

CDB5376
2.3.6 RS-485 Telemetry
By default, CDB5376 communicates with the PC evaluation software through the microcontroller USB
port. Additional hardware is designed onto CDB5376 to use the microcontroller I2C port as a low-level
local telemetry, but it is provided for custom programming convenience only and is not directly supported
by the CDB5376 PC evaluation software or microcontroller firmware.
Telemetry signals enter CDB5376 through RS-485 transceivers, which are differential current mode trans-
ceivers that can reliably drive long distance communication. Data passes through the RS-485 transceiv-
ers to the microcontroller I2C interface and the clock and synchronization inputs.
Specification
RS-485 Transceiver - Linear Tech
Surface Mount Package Type
Supply Voltage, Quiescent Current
Maximum Data Rate
Transmitter Delay, Receiver Delay
Transmitter Current, Full Termination (60 Ω)
Transmitter Current, Half Termination (120 Ω)
Value
LTC1480IS8
SOIC-8, 5mm x 6mm
3.3V, 600 µA
2.5 Mbps
25 - 80 ns, 30 - 200 ns
25 mA
13 mA
2.3.6.1 CLK, SYNC
Clock and synchronization telemetry signals into CDB5376 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.
Specification
Synchronous Inputs, 2 wires each
Specification
Distributed SYNC Signal Synchronization
Distributed Clock Synchronization
Analog Sampling Synchronization Accuracy
Value
CLK±, SYNC±
Value
± 240 ns
± 240 ns
± 480 ns
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 J56. 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_MC signal output to the digital filter SYNC input as required.
DS612DB2
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