Flowserve DDC-100 Modbus Direct-to-Host User Manual download pdf (Page 22)

38 DDC-100 Direct-to-Host Programming Guide FCD LMAIM4019-00 FCD LMAIM4019-00 DDC-100 Direct-to-Host Programming Guide 39

Example 4: Loss of 1 of 2 Host Ports

The Host is attempting to communicate with the ﬁeld units via both ports but is unable to reach

any ﬁeld units via port 2. This typically indicates a broken cable connection at port 2 or at the ﬁrst

ﬁeld unit from port 2, broken or shorted cable between the Host and the ﬁrst ﬁeld unit from port 2,

improperly terminated wires, or loss of power to the RS-232/485 converter if attached to the Host

port 2.

Non-Looped Network Truth Table via Port 1 (Channel A) Polling Only Summarizing the results

of Examples 5 through 7: Recorded in Host ﬁeld unit Status Register bit 10. Bit 11 Channel B is

always 0 as set by the Host

Field unit #

Example 5 Example 6 Example 7

Ch. A Ch. B Ch. A Ch. B Ch. A Ch. B

1 0 0 0 0 0 0

2 0 0 1 0 0 0

3 0 0 0 0 1 0

4 0 0 0 0 1 0

5 0 0 0 0 1 0

Example 5: No faults

The Host is successfully communicating with each ﬁeld unit and sets the bit equating to Channel A

Fault to 0. A value of 0 in the Channel A Fault bit indicates successful communication.

Example 6: A ﬁeld unit is off-line

The Host is successfully communicating with ﬁeld units 1, 3, 4, and 5. Field unit 2 does not

respond, causing the Host to set ﬁeld unit 2 Channel A Fault to 1. In this example, ﬁeld unit 2 is

without power, causing the ﬁeld unit 2 network board bypass relays to de-energize. This de-ener-

gization of the bypass relays shorts the signal through the network board and isolates the ﬁeld unit

from the DDC-100 Network.

Example 7: A break or short in the network

The Host is successfully communicating with ﬁeld units 1 and 2 but is not able to communicate

with ﬁeld units 3, 4, and 5, causing the Host to set ﬁeld unit 3, 4, and 5 Channel A Fault to 1. This

typically indicates a broken or shorted cable between ﬁeld unit 2 and 3, a broken cable connection

at ﬁeld units 2 or 3, improperly terminated wires at ﬁeld unit 2 or 3, or loss of power to ﬁeld units 3,

4, and 5.

4.4 Network Control

4.4.1 Ladder Logic Routines

The PLC running a ladder logic program is capable of being an integral part of any valve actuator

network. All commands for network polling and valve positioning may be generated by the PLC

and sent through a Modbus Master communications port to the valve actuator network. This port

is typically located on a PLC component or installed on a PLC-compatible third party Modbus

interface module. These modules may contain either one or multiple Modbus ports.

Examples of this type of interface include, but are not limited to A-B PLC-5, A-B SLC-500, Square

D PLC, Modicon 984, Modicon Quantum, Compact or Micro PLC, Siemens S5 115U, or Simatic

TI-545/555.

4.4.2 Software Control Modules (C++ or Visual Basic Program)

The use of Visual Basic or C++ allows the user to totally customize the individual application to

meet application speciﬁc requirements. The user can create a functional speciﬁcation that a system

integrator can use to write a unique user-interface for polling and commanding the valve actuator

network. All Modbus commands for polling or commanding are implemented in a user-developed

software driver.

The advantage of this method of control is that any system integrator familiar with process control,

Visual Basic, or C++ can write a unique application. This approach provides the user with ﬂexibility

to use the software at many sites without repeatedly purchasing site licenses for Modbus driver

software or application packages.

4.4.3 Personal Computer with a Graphical User-Interface

A Graphical User-Interface (GUI) software package can be used to communicate directly with the

DDC-100 Network without communicating through a dedicated data concentrator. This control

of the network requires a Modbus Driver for the GUI that is compatible with the Modbus function

codes supported by a DDC-100 Field Unit. The network communication will follow the polling and

command rules established by the individual application.

Most GUI Modbus drivers do not toggle the PC RS-232 serial port RTS/DTR line. The Limitorque

Self-Steered RS-232/485 converter will enable communication between the PC and the DDC-100

Network.

Examples of GUIs include, but are not limited to, Wonderware InTouch, PCSoft Wizcon, Intellution

FixDMACS, and Genesis Iconics.

NOTE: This category of off-the-shelf, PC-based software also includes numerous Supervisory

Control and Data Acquisition (SCADA), Human Machine Interface (HMI), and Hybrid real-time

system conﬁguration and development software packages.

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