Rockwell Automation T7150A User Manual

ICS Regent + Plus

PD-7002

Communications Modules

RS-232, RS-422 and RS-485

(T7150A)

Issue 1,

Communications modules provide a serial communications interface between the controller and external equipment. Communications modules are commonly used to connect the controller to the computer running the application, serial printers, man-machine interfaces, distributed control system gateways, and other peer-to-peer controllers.

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March, 06

Features

Two isolated serial ports per module.

Supports RS-232, RS-422 and RS-485 standards.

•

Regent R2, Guarded Peer-Link, and Modbus protocols.

Front panel indicators on each module show communi status and transmit/receive activity.

TÜV certified for safety, Risk Class 5.

Module Operation

A block diagram of a typical communications module is shown in Figure 1.

Communications modules are serial receiver-transmitters that provide an electrical interface for RS-232, RS-422, and RS-485 communications equipment.

Each communications module receives power from all three of the processor modules. A power-sharing circuit communications modules receives the power from the three

cations

in each of the

Industrial Control Services

Communications Modules

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processor modules and combines it through a diode OR power sharing circuit. This ensures that if one processor module's power supply fails, the communications module will continue to operate by drawing power from the two remaining power supplies, and the system's communications functions are maintained.

Additional isolated power converters provide isolated power to the two serial ports. This isolation provides protection from external from affecting module operations.

communications cable signal noise and grounding

Figure 1. Block Diagram of Communications Module.

The Dual UART (universal asynchronous receiver/trans

mitter) buffers incoming and outgoing communications characters. The triplicated processor modules interrupt once

Industrial Control Services

Communications Modules

(T7150A)

every millisecond to read characters from or write characters to the communications module.

When the processor modules read characters from the communications module, the communications module sends characters through triplicated bus drivers to the processor Safetybus. The processor modules vote this triplicated data and perform communications processing. When the processor modules write data to the communications module, the triplicated data is voted by the communications modules and sent to the dual UART where it is then transmitted out the associated port.

The communications modules’ two serial ports operate independently and can both be configured differentl

y. Electrical configuration is done by changing jumper settings to select point-to-point or multidrop configurations. The ports can be used to support a wide variety of functions including Regent R2 protocol, Modbus protocol, ASCII output, and Guarded Peer-Link communications. The

INTERPRET

application is used to configure the appropriate port functions and specify baud rate, data format, parity, and node number.

Testing and Diagnostics

The modules triplicated Safetybus interface ensures that no failure in the module will effect the operation of the Regent system or other module. Extensive fault detection and annunciation of critical redundant circuits helps ensure that processors will not accept erroneous data from a faulty module.

Each type of communications module has a unique identification code that is read by the controller. This code lets the controller know what type of module is installed in each communications slot. If a module is removed and replaced with a module of a different type the pro indicate a COMM error.

cessors will

The processor modules perform background diagnostic checks on the module to test bus driver circuits and check the communications module ID codes. Communications message format, framing, checksum, and other communications errors

PD-7002

Mar-06

Communications Modules

are checked by the processor modules’ normal communications processing.

Failures result in a COMM module error indication at the processor modules and a COMM error at the communications module.

(T7150A)

Front Panel

Figure 2 shows t

he physical features of the communications modules. The front panel of each module contains indicators showing overall module health, and the transmit and receive status of each channel. In addition to the front panel indicators, each communications module has two DB-25 connectors (female).

COMM Indicator

This red and green LED pair indicates the overall health of the module. During normal operation the green LED is on. If a communications module fault is detected, the red LED turns on and the green LED

Transmit/Receive Indicators

turns off.

These green LEDs are connected directly to the serial signal lines and flash while data are being transmitted or received. The TX LED flashes as data are sent from the module, and the RX LED flashes as data are received by the module.

Industrial Control Services

Communications Modules

(T7150A)

PD-7002

Mar-06

Figure 2. Communications Module.

Pin No.

RS232

Signal

RS422/485

Signal

2 TX

(not used)

3 RX

(not used)

GND

(not used)

+ 5 VDC

(not used)

TX (-)

(not used)

RX (-)

(not used)

TX (+)

(not used)

RX (+)

Communications Modules

(T7150A)

Application

Communications Port Connections

Each communications port has a DB-25, female connector on the front of the module. The RS232 and RS422/485 signals are internally connected to the DB-25 connector pins as shown in Table 1. Refer to Figures 3 through 5 for recommended communications cable requirements and connections.

Table 1. Communications Port Pin-out.

Recommended Ca

For multidrop and Guarded Peer-Link communications a Belden cable type 813x (where x = number of pairs) is recommended. The cable has the following characteristics that are important:

120 Ohm, Characteristic Impedance Twisted Pairs Overall shield

Communications Configurations

The communications module supports a variety of communications configurations which are shown in Figures through 5. Figure 3 illustrates two point-to-point

ble Type

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Communications Modules

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configurations, one using RS232 connections for short distances and the other using RS422 connections for longer distances. Figure 4 illustrates multidrop connections between 2 or more Regents and a PC or other communications device supporting Regent R2 or Modbus protocols. Figure

5 illustrates multidrop connections between 2 or more Regents using the Guarded Peer-Link protocol.

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Figure 3. Point-to-P

oint Communications.

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