ABB Zenith MX350 Use and care manual

—

COMMUNICATIONS GUIDE

Zenith MX350

Microprocessor Controller for ZTE series

Automatic Transfer Switches

ABB MX350 Automatic Transfer Control System Communications Guide for revision

1.2x.

EnerVista, EnerVista Launchpad, EnerVista MX350 Setup, and FlexLogic are registered

trademarks of The General Electric Company.

The contents of this manual are the property of ABB Inc. This documentation is of ABB.

furnished on license and may not be reproduced in whole or in part without the permission

of ABB. The content of this manual is for informational use only and is subject to change

without notice.

Part number: 1601-9072-A3 (April 2010)

TABLE OF CONTENTS

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Table of Contents

Communications interfaces .........................................................................................1

RS485 interface (Modbus RTU) .....................................................................................2

Modbus Protocol...............................................................................................................................................2

Electrical Interface .......................................................................................................................................... 2

Data Frame Format and Data Rate ........................................................................................................ 2

Data Packet Format ....................................................................................................................................... 2

Error Checking................................................................................................................................................... 3

CRC-16 Algorithm ............................................................................................................................................3

Timing.................................................................................................................................................................... 4

MX350 supported functions ....................................................................................................................... 4

Modbus Functions............................................................................................................................................5

Function Code 01H ......................................................................................................................................... 5

Function Code 03H ......................................................................................................................................... 6

Function Code 04H ......................................................................................................................................... 7

Function Code 05H ......................................................................................................................................... 8

Function Code 06H .......................................................................................................................................10

Function Code 08H .......................................................................................................................................10

Function Code 10H .......................................................................................................................................11

Error Responses..............................................................................................................................................11

Performing commands using Function Code 10H ........................................................................ 12

Using the User Definable Memory Map ..............................................................................................13

Modbus memory map.................................................................................................................................14

Format codes .................................................................................................................................................. 44

Ethernet interface........................................................................................................66

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TABLE OF CONTENTS

1EDIUGSNOITACINUMMOC–METSYSLORTNOCREFSNARTCITAMOTUA053XM

MX350 Automatic Transfer Control

System

Communications Guide

Communications interfaces

The MX350 supports two communications interfaces:

• Modbus RTU via RS485

• Modbus TCP/IP via 10/100Base-T Ethernet

In addition, a USB interface is provided on the front of the interface panel. It is configured

to be used in conjunction with a virtual serial port on a Windows-based PC.

NOTE: Setpoint changes related to communication parameters require a power cycle of the

controller to be activated.

NOTE: For full details, please refer to the MX350 Communications Guide to be found at http://

www.gedigitalenergy.com/app/Resources.aspx?prod=zte&type=3 .

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RS485 interface (Modbus RTU)

The RS485 interface is a serial two-wire port intended for use as a Modbus RTU slave. The

RS485 port has the following characteristics.

• Address: 1 to 254, default 254

• Baud rate: 9600 to115200 bps, default 115200

• Parity: None

• Data bits: 8

• Stop bits: 1

• Supported Modbus function codes: 1, 3, 4, 5, 6, 7, 8, 16

Modbus Protocol

The MX350 implements a subset of the Modicon Modbus RTU serial communication

standard. The Modbus protocol is hardware-independent. That is, the physical layer can be

any of a variety of standard hardware configurations. This includes RS232, RS422, RS485,

fibre optics, etc. Modbus is a single master / multiple slave type of protocol suitable for a

multi-drop configuration as provided by RS485 hardware. The MX350Modbus

implementation employs two-wire RS485 hardware. Using RS485, up to 32 MX350s can be

daisy-chained together on a single communication channel.

The MX350 is always a Modbus slave. It can not be programmed as a Modbus master.

Computers or PLCs are commonly programmed as masters.

Both monitoring and control are possible using read and write register commands. Other

commands are supported to provide additional functions.

Electrical Interface The hardware or electrical interface in the MX350 is two-wire RS485. In a two-wire link,

data is transmitted and received over the same two wires. Although RS485 two wire

communication is bi-directional, the data is never transmitted and received at the same

time. This means that the data flow is half duplex.

RS485 lines should be connected in a daisy chain configuration with terminating networks

installed at each end of the link (i.e. at the master end and at the slave farthest from the

master). The terminating network should consist of a 120 W resistor in series with a 1 nF

ceramic capacitor when used with Belden 9841 RS485 wire. Shielded wire should always

be used to minimize noise. The shield should be connected to all of the MX350s as well as

the master, then grounded at one location only. This keeps the ground potential at the

same level for all of the devices on the serial link.

NOTE: Polarity is important in RS485 communications. The '+' (positive) terminals of every device

must be connected together.

Data Frame Format

and Data Rate

One data frame of an asynchronous transmission to or from a MX350 typically consists of

1 start bit, 8 data bits, and 1 stop bit. This produces a 10 bit data frame. This is important

for transmission through modems at high bit rates (11 bit data frames are not supported

by Hayes modems at bit rates of greater than 300 bps).

Modbus protocol can be implemented at any standard communication speed. The

MX350supports operation at 9600, 19200, 38400, 57600, and 115200 baud.

Data Packet Format A complete request/response sequence consists of the following bytes (transmitted as

separate data frames):

Master Request Transmission:

SLAVE ADDRESS: 1 byte

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FUNCTION CODE: 1 byte

DATA: variable number of bytes depending on FUNCTION CODE

CRC: 2 bytes

Slave Response Transmission:

SLAVE ADDRESS: 1 byte

FUNCTION CODE: 1 byte

DATA: variable number of bytes depending on FUNCTION CODE

CRC: 2 bytes

SLAVE ADDRESS: This is the first byte of every transmission. This byte represents the user-

assigned address of the slave device that is to receive the message sent by the master.

Each slave device must be assigned a unique address and only the addressed slave will

respond to a transmission that starts with its address. In a master request transmission the

SLAVE ADDRESS represents the address of the slave to which the request is being sent. In a

slave response transmission the SLAVE ADDRESS represents the address of the slave that is

sending the response.

FUNCTION CODE: This is the second byte of every transmission. Modbus defines function

codes of 1 to 127.

DATA: This will be a variable number of bytes depending on the FUNCTION CODE. This may

be Actual Values, Setpoints, or addresses sent by the master to the slave or by the slave to

the master.

CRC: This is a two byte error checking code.

Error Checking The RTU version of Modbus includes a two byte CRC-16 (16 bit cyclic redundancy check)

with every transmission. The CRC-16 algorithm essentially treats the entire data stream

(data bits only; start, stop and parity ignored) as one continuous binary number. This

number is first shifted left 16 bits and then divided by a characteristic polynomial

(11000000000000101B). The 16 bit remainder of the division is appended to the end of the

transmission, MSByte first. The resulting message including CRC, when divided by the

same polynomial at the receiver will give a zero remainder if no transmission errors have

occurred.

If a MX350 Modbus slave device receives a transmission in which an error is indicated by

the CRC-16 calculation, the slave device will not respond to the transmission. A CRC-16

error indicates than one or more bytes of the transmission were received incorrectly and

thus the entire transmission should be ignored in order to avoid the MX350performing any

incorrect operation.

The CRC-16 calculation is an industry standard method used for error detection. An

algorithm is included here to assist programmers in situations where no standard CRC-16

calculation routines are available.

CRC-16 Algorithm Once the following algorithm is complete, the working register “A” will contain the CRC

value to be transmitted. Note that this algorithm requires the characteristic polynomial to

be reverse bit ordered. The MSBit of the characteristic polynomial is dropped since it does

not affect the value of the remainder. The following symbols are used in the algorithm:

—>: data transfer

A: 16 bit working register

AL: low order byte of A

AH: high order byte of A

CRC: 16 bit CRC-16 value

i, j: loop counters

(+): logical exclusive or operator

Di: i-th data byte (i = 0 to N-1)

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G: 16 bit characteristic polynomial = 1010000000000001 with MSbit dropped and bit order

reversed

shr(x): shift right (the LSbit of the low order byte of x shifts into a carry flag, a '0' is shifted

into the MSbit of the high order byte of x, all other bits shift right one location

The algorithm is:

1. FFFF hex —> A

2. 0 —> i

3. 0 —> j

4. Di (+) AL —> AL

5. j+1 —> j

6. shr(A)

7. is there a carry? No: go to 8. Yes: G (+) A —> A

8. is j = 8? No: go to 5. Yes: go to 9.

9. i+1 —> i

10. is i = N? No: go to 3. Yes: go to 11.

11. A —> CRC

Timing Data packet synchronization is maintained by timing constraints. The receiving device

must measure the time between the reception of characters. If 3.5 character times elapse

without a new character or completion of the packet, then the communication link must

be reset (i.e. all slaves start listening for a new transmission from the master). Thus at 9600

baud a delay of greater than 3.5 x 1 / 9600 x 10 x = x 3.65 x ms will cause the

communication link to be reset.

MX350 supported

functions

The following functions are supported by the MX350:

• FUNCTION CODE 01 - Read Input Status

• FUNCTION CODE 03 - Read Setpoints and Actual Values

• FUNCTION CODE 04 - Read Setpoints and Actual Values

• FUNCTION CODE 05 - Execute Operation

• FUNCTION CODE 06 - Store Single Setpoint

• FUNCTION CODE 07 - Read Device Status

• FUNCTION CODE 08 - Loopback Test

• FUNCTION CODE 10 - Store Multiple Setpoints

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Modbus Functions

Function Code 01H Modbus implementation: Read Input Status

MX350 implementation: Read Net Control Status

This function code is supported for a selective range of commands for MX350 for net

control functionality. This function reads the ON/OFF status for each net control

command. The query message specifies the starting command and number of commands

status to be read. Commands are addressed starting at zero.

The master/slave packets have the following format:

Table 1: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 03H

Each returned data bit is an ON/OFF status. The number of returned data bytes will

change according to the number of points requested.

The following table lists the supported command addresses for this function code:

MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION

SLAVE ADDRESS 1 11 message for slave 17

FUNCTION CODE 1 02 read net control status

STARTING ADDRESS 2 00 C4 starting command address

NUMBER OF POINTS 2 00 02number of statusbits

edocrorreCRC1CRC

SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION

SLAVE ADDRESS 1 11 message from slave 17

FUNCTION CODE 1 02 read net control status

BYTE COUNT 1 01 number of status bytes

suta

tslortnoctenfosetyb11ATAD

edocrorreCRC1CRC

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Function Code 03H Modbus implementation: Read Holding Registers

MX350 implementation: Read Setpoints

For the MX350 implementation of Modbus, this function code can be used to read any

setpoints (“holding registers”). Holding registers are 16 bit (two byte) values transmitted

high order byte first. Thus all MX350Setpoints are sent as two bytes. The maximum

number of registers that can be read in one transmission is 125.

The slave response to this function code is the slave address, function code, a count of the

number of data bytes to follow, the data itself and the CRC. Each data item is sent as a two

byte number with the high order byte sent first.

For example, consider a request for slave 17 to respond with 3 registers starting at address

006B. For this example the register data in these addresses is as follows:

noitpircseDrebmuNdnammoC

retnuoCelbaliavA2SemiTteseR691

ecneliSmralA791

remit-WssapybotlortnoC891

remit-TssapybotlortnoC991

daoloNnotseTlrtCteN002

lortnoCtseTdaoLtsaF102

lortnoCtseTdaoLralugeR202

SotrefsnarterlaunaM/otuA302

2S/1SotrefsnartlaunaM/otuA402

1SrofdehSdaoLlrtCteN502

2SotrefsnarTtibihnIlrtCteN602

1SotrefsnarTtibihnIlrtCteN702

rotceleSedoMnoitisnarTlrtCteN802

05RssapyBotdnammoC902

05RssapyBmrifnoC012

05RssapyBlecnaC112

resicrexEgnidnePssapyB212

ssapyBresicrexElecnaC312

tibihnIrefsnarTotuAlrtCteN412

yaleRrefsnarTotuAlrtCteN512

remiTSTAevitcAssapyB

lrtCteN612

lecnaCresicrexElrtCteN712

tratSrotareneGlrtCteN812

potSrotareneGlrtCteN912

2SrofdehSdaoLlrtCteN022

noitceleSecruoSemirPlrtCteN122

lecnaCedoMtseTlrtCteN222

daoLnOtseTlrtCteN322

timmoCrefsnarTlrtCteN422

ataDsserddA

B220B600

0000C600

4600D600

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