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Communicate with I/O
Communicate with
FOUNDATION Fieldbus
Devices
Chapter 5
The 1757-FFLD linking device bridges an EtherNet/IP network to
FOUNDATION Fieldbus links.
EtherNet/IP Network
ControlLogix Controller
1756-FFLD Device
FOUNDATION Fieldbus Network
509 -BOD
24vdc
T
Guideline
Description
Each 1757-FFLD device supports 16 Logix
exchange function blocks.
Each Logix exchange function block supports eight analog inputs and eight analog outputs.
Each function block uses one CIP connection.
One 1756-ENBT communication module supports 125 CIP connections, which in turn
supports seven 1757-FFLD devices that each have 16 function blocks. Add another
1756-ENBT module to support additional 1757-FFLD devices.
The type of device affects the maximum
number of FOUNDATION Fieldbus devices
per H1 segment.
Each 1757-FFLD device supports two or four H1 segments.
Do not exceed the maximum number of
virtual communication relationships (VCRs)
on each H1 segment.
A VCR is a channel that provides for the transfer of data between FOUNDATION Fieldbus
devices. The number of VCRs required to send data or receive data depends on the device
and type of data.
• 8...10 instruments (16 maximum) per each H1 segment.
• For valves, 4...6 per segment because valves have more data.
The 1757-FFLD supports a maximum of 16 publisher and 16 subscriber VCRs for each H1
segment. Each parameter you pass to or from the Logix5000 controller uses a VCR. Some
devices, such as valves, use more VCRs than transmitters.
Make sure you have the correct device
description (DD) for each FOUNDATION
Fieldbus device.
DDs are like EDS files for DeviceNet devices. You can find DDs on vendor/organization
websites or on media that ships with the device. A host with DD services can interoperate
with all parameters defined in the DD for a field device.
Use the right wiring and connection
products.
Always use a tree or modified tree topology. Never daisy chain devices.
Noise is the most frequent problem, due to:
• wrong wiring.
• improper grounding.
• bad connectors.
To get the best implementation, understand
the details of a FOUNDATION Fieldbus
system.
Publication 1756-RM094C-EN-P - June 2007
See these references:
• FOUNDATION Fieldbus Technical Overview at http://www.fieldbus.org
• RelcomWiring Guide at http://www.relcominc.com
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