Flowserve DDC-100 Modbus Direct-to-Host User Manual download pdf (Page 16)

26 DDC-100 Direct-to-Host Programming Guide FCD LMAIM4019-00 FCD LMAIM4019-00 DDC-100 Direct-to-Host Programming Guide 27

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The DDC-100

Network

The Flowserve Limitorque DDC-100 Network is a digital communications network based on

non-proprietary hardware and protocols. This network is capable of maintaining up to 250 valve

actuators or other devices over a simple shielded, twisted-pair connection. The network consists

of a master (Host PLC, Host Computer, Limitorque Master Station, or some other Master-capable

device) and a number (up to 250) of ﬁeld units. The EIA RS-485 standard is used for the physical

interface between devices to provide reliable communications over long distances.

Two protocols are supported by Limitorque Field Units—Modbus® and BITBUS®. The protocol

must be speciﬁed when the units are ordered; however, the protocol may be changed in the ﬁeld

(requires new EPROM). The Modbus protocol was developed by AEG Modicon and the BITBUS

protocol was developed by the Intel Corp. Modbus protocol is more widely used, has a simpler

implementation, and satisﬁes most applications that are not extremely time-critical. Therefore, this

document addresses only the Modbus protocol. BITBUS protocol information is available upon

request.

NOTE: The MX-DDC does not support Bitbus protocol.

The network cable connects the ﬁeld unit to the Host System. Belden 3074F, 3105A, and 9841

shielded, twisted-pair cable should be used. The use of other cables may result in a reduction of

internodal distances or increased error rate. Other individually shielded, twisted-pair cables with

electrical properties within 5% of the recommended Belden cables may be used but have not been

performance-tested with the DDC-100 Network.

Belden 3074F Speciﬁcations

• Total cable length between repeaters or nodes with repeaters: up to 19.2 kbps: 5000' (1.52 km)

For loop mode, this is the total length between operating ﬁeld units. If a ﬁeld unit loses power,

relays internal to the ﬁeld unit connect the A1 Channel to the A2 Channel, which effectively doubles

the length of the cable (assuming a single ﬁeld unit fails). If you need to assure operation within

speciﬁcations in the event of power failure to ﬁeld units, then this consideration must be added.

Example: To assure operation within speciﬁcation when any two consecutive ﬁeld units lose power,

then the maximum length on cable up to 19.2 kbps: 5000' (1.52 km) per every four eld units.

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Flowserve DDC-100 Modbus Direct-to-Host User Manual Page 16