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Redundancy Made Easy

The Redundant Serial Interface consists of a pair of serial

cards and a redundant terminal block. The cards each

contain two serial communications ports that support

RS422/485 half duplex (in either single slave or multi-drop

configurations), or RS422/485 full duplex (in single slave

configuration only), as well as RS232. These ports are

individually configurable and support data rates up to

115 KBaud.

Slave devices must provide two serial ports in order to allow

the active and standby serial cards to be connected. The

Active card continually poll input data and writes output

data to the device on one serial link, while the standby card

periodically polls the slave device for a diagnostic register.

Verify with the device supplier for its ability to support

redundant Modbus serial communications.

When a fault is detected, the system automatically

switches to the backup serial card. Events that can cause a

switchover include:

• Hardware failure within the active card

• Loss of Communications (including field cable and

slave port problems) between the active card and the

slave device

• Removal of the active card from the carrier

A switchover may also be initiated from control logic. This

allows additional watchdog logic to monitor multiple slave

devices for communication faults not detected by the

Serial Interface. A manual switchover can be initiated from

diagnostics explorer.

The serial card supports the input and/or output of

16 different data sets per serial port, for a total of 32 data sets

per Serial Interface.

Serial dataset registers can be referenced directly in control

modules as analog or discrete I/O providing fast easy data

exchange with the serial device. Direct module-to-Dataset/

register references are recommended for control signals.

Alternatively, users can read multiple registers form a

Dataset into a single “marshalling” module at the cost of

a single DST. Marshalling modules provide a cost effective

way to integrate serial data from analyzers and other data

sources. Serial dataset registers can also be passed as

SCADA values directly to Workstations and Continuous

Historians without consuming DST’s.

Both Modbus RTU and Modbus ASCII communications

modes are supported by standard Modbus protocol.

The serial card supports the following features using the

Modbus protocol:

• Reading input data from Modbus coils, input status,

holding registers and normal input registers.

• Writing output data to coils and holding registers.

• Output data can be written in single coil, register mode,

or complete data set mode. This output mode is a

configurable parameter.

• Input data can be read in as a complete data set,

providing the best performance.

The serial card supports the input and/or output of

16 different data sets per serial port, for a total of 32 data sets

per Serial Interface.

Serial dataset registers can be referenced directly in control

modules as analog or discrete I/O providing fast easy data

exchange with the serial device. Direct module-to-Dataset/

register references are recommended for control signals.

Alternatively, users can read multiple registers form a

Dataset into a single “marshalling” module at the cost of

a single DST.

Product Description

The Serial Interface consists of a serial card and a terminal

block. The card contains two serial communications

ports that support RS232 and RS422/485 half duplex, or

RS422/485 full duplex signals. These ports are individually

configurable and support data rates from 300 Baud up to

115 KBaud.

The S-series card plugs into an 8-wide I/O carriers in any of

the possible 64 slots and communicates with the S-series

controllers. LEDs, located on the front of the card, show the

power, error, and port status of the interface at a glance.

The standard Modbus protocol includes the Serial Interface,

the Modbus RTU, and ASCII communications protocol

as defined in the Modicon Modbus Protocol Reference

Manual dated March 1992 (PI-MBUS-300 REV D). Each Serial

Interface port may be configured as either a master or

slave device.

1:1 Redundancy for Serial I/O cards. You can add

Serial interfaces as simplex cards or redundant pairs.

The interfaces automatically detect the presence of

the redundant terminal block and are autosensed by

the system as a redundant pair. There is no additional

configuration. Use redundant Serial interfaces with slave

devices that support redundant serial ports.

Automatic switchover. Should a primary Serial

Interface card fail, the system automatically switches

to the “standby” card without user intervention. The

operator is given clear notification of a switchover at the

operator display. The standby card continually polls the

slave devices for diagnostic to confirm its ability to take

over communications.

Benefits

Provides seamless information interface. Using

the Serial Interface with the DeltaV system, you gain an

extended view of your entire plant. All serial information

from 3rd party systems, analyzers, PLC’s, is readily available

for display at the Operator Interface.

When connected to a PLC, DeltaV software may pass

supervisory information to the PLC facilitating the

coordination of control strategies across systems.

Plug-and-play easy to use. Plug-and-play installation

saves money. The Serial Interface works just like other

DeltaV I/O interfaces. It fits into any available slot on the

controller I/O carrier. There are no dipswitches. Just plug it in!

The DeltaV controller auto-senses the Serial Interface and

presents the configuration options. Online help makes this

interface a snap to configure. After a simple point-and-click

configuration exercise, your integrated solution is up and running.

The DeltaV™ S-series Serial Interface provides a connection between the DeltaV system and other

devices.

• Provides seamless information interface

• Plug-and-play ease of use

• Extends the life of existing equipment

• 1:1 redundancy for Serial Interface I/O cards

• Automatic switchover

Introduction

The S-series Serial Interface provides a connection

between the DeltaV™ system and devices that support a

serial protocol, such as Modbus or Allen Bradley’s Data

Highway Plus.

The S-series Serial Interface is supplied with Modbus

software drivers pre-loaded. Additional drivers are available

to allow a wide variety of devices to be integrated directly

into the DeltaV controller’s I/O subsystem. Data can be used

by control modules or communicated to workstations as

SCADA tags for display and/or historizing. Like all DeltaV I/O,

the Serial Interface may be added online while the rest of

the controller I/O is powered up and in use.

DeltaV Serial Interface can also be installed as a redundant

pair for critical applications needing the highest availability.