Flowserve MX-100 Field Unit - Manual (Page 10)

MX/DDC-100 Field Unit Installation and Maintenance FCD LMENIM2329-01 – 03/11
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2.2.3 Host Controller
In the DDC-100 system, the network can be connected directly to a host controller without an interposing Master
Station II.
In this configuration, the host sends commands and messages to, and gathers responses from, the field units. The
commands and messages are sent via RS-485 data signals. The gathered responses are stored in a data table in the
host and are periodically updated by sequential polling of the field units. The host controls up to 250 field units. See
Section 3.1.2.3, Network Cable Connection to Host System or Master Station II.
When a host controller is used to directly communicate with the field units, i.e., direct-to-host communications, it
communicates using the Modbus protocol and the RS-485 electrical standard. This host controller can be one of the
following:
Distributed control system (DCS) •
Programmable logic controller (PLC) •
Personal computer (PC) •
Plant Asset Management (PAM) system •
Figure 2.3 – Typical direct-to-host arrangement
DCS PC/PAM PLC
1 250
5 2
3 4
RS-485