modbus communication

Modbus communication

Schneider Electric 2- PMC – C.Alépéé – 2009/01/05

RS485 Modbus

RS232 RS 485

? =S= communication architecture

Ethernet

RS232

Port COM du PC

RS485 Modbus

PC

net

wo

rk b

oar

d

RS485 Modbus

gateways

Internet

Host B

PSIN, ISDN, ADSL

PSIN, ISDN, ADSL@

Internet

Host B

PSIN, ISDN, ADSL

PSIN, ISDN, ADSL@


Communication = exchange of several types of information

Logical, digital information (O/C)

for alarms and testing

● circuit breaker status

● alarms

● protection unit status

● earthing switch status

Sepam Sepam Sepam

Analog information

● measurements

● counters

● remote readings and settings

● disturbance readingsfor power monitoring/management

SCADA


Sepam data exchanged● The measurements presented in a

Sepam depend on the type of Sepam.● Measurement readout● phase currents,● line to line voltages, frequency,● real and reactive power, and power

factor,● accumulated real and reactive energy,● peak demand phase current,● peak demand real and reactive power,● tripping currents,● temperatures, thermal capacity used,● number of starts and inhibit time,● running hours counter.

● Readout of program logic resource status

● event counter values,● logical input status,● status of the remote annunciation bits

(TS).● Remote control● writing of remote control orders (TC)● Other functions● time tagging,● remote reading of Sepam settings

(remote reading),● remote setting of protections and control

logic time delays (remote setting);● transfer of disturbance recording data.


Example: Modbus

Network concept

e.g. TCP/IP

DATA LINKLAYER

2

Data transmission

NETWORKLAYER

3

Data processing

TRANSPORTLAYER

4

SESSIONLAYER

5

APPLICATIONLAYER 7

End-to-end management

Network interconnection

- OSI: 7-layer architectureOSI = Open Systems Interconnection

PHYSICALLAYER

1

PRESENTATION LAYER 6

Bus concept:

RS 485 & 232

Ethernet


- topology between components

Point to point

Star

Bus

Ring

Meshed


- type of transmission

Full duplex transmission: simultaneous two-way

Half duplex transmission: alternating two-way

Simplex transmission: one-way


- transmission mode

Serial bus

0

1

0

Parallel bus

Number of bits sent simultaneously

StartStop

– Synchronous:

– Asynchronous:

10 0 1

clock = continuous transmission

irregular transmission

Data

01 10 0 0 1 1

1 character


Asynchronous transmission mode (cont'd)

Need for a communication format

● start = initializes the communication frame, indicates the start of the message.

● useful data bits = useful data bits of the message.

● error check = to check for transmission errors.

● stop = indicates the end of the message.

0

1 start useful data bits error check stop

communication frame


- medium Distance: maximum length, line losses

Rate = cable capacity

Type of communication chosen: RS 485 or Ethernet

Price

Environment (EMC, Temperature, etc.)

Twisted pair cable

Simple to implement

Low cost


RS232 RS485

RS 485 Modbus

PC COM Port

- physical layer standards: RS232 and RS485

0 +5 +15V 1.5 + 5V1 - 5 - 15V - 1.5 - 5V

19200 Bauds 1Mbauds

30 m 1200 m

RTS/CTS No

Multipoint busHalf duplex

Point to Point

Asynchronous

Electrical levels

Max. rate

Length

(flows)

Control lines

Link

PC devicesDATA LINKLAYER

2

NETWORK LAYER

3

TRANSPORTLAYER

4

SESSIONLAYER 5

APPLICATIONLAYER 7

PHYSICAL LAYER

1



2-wire bus topology


4-wire bus topology


RS485 signal


Communication Settings

● Sepam address

● Speed

● Parity


Sepam series 20 40 80 communication Interfaces

Module ACE 949-2

Sepam connection to a Modbus 2 wires network

Module ACE 959

Sepam connection to a Modbus 4 wires network

Module ACE 937

Sepam connection to a Modbus optical fiber network


ACE 969 interface Sepam series 20 40 80double port plus DNP3 and IEC 870 5 103protocol

ACE969-2TP ACE969-2FO


ACE 909-2 Convertor

Division - Na me - Date - L angu age 50

Installation and Quick StartRS485 / RS232 converter - ACE909-2

RS485 2 wire

Remote power source: the ACE909-2 converter supplies 12 V - 24 V ( ACE949 -959 / SEPAM 1000+ )

RS485 connection RS232 link

Ph/N powerSelector 12 or 24vdc

Fuse

Speed SW2/1 SW2/2 SW2/31200 1 1 12400 0 1 14800 1 0 19600 0 0 119200 1 1 038400 0 1 0

strap position functionSW2/4 0 with parity

1 without paritySW2/5 1 2 stop

0 1 stop

SW1/1 ON polarization at 0 V via Rp - 470 Ω

SW1/2 ON polarization at 5 V via Rp +470 ΏSW1/3 ON 150 Ώ impedance matching resistor at end of RS485 Bus


ACE 919 Convertor

Division - Name - Date - Lan guag e 51

Installation and Quick StartRS485 / RS485 converter - ACE919

supply voltageselection switch110 V AC or 220V AC

RS485 2 wire

Remote power source: the ACE919 convertersupplies 12 V - 24 V (ACE949 - 959 / SEPAM 1000+ )

ACE 919 CC 24 - 48 V DCACE 919 CA 110 - 220 V AC

Strap position function

SW1/1 ON polarization at 0V via Rp-470Ώ

SW1/2 ON polarization at 5V via Rp+470Ώ

SW1/3 ON 150 Ώ impedance matching

resistor at end of RS485 bus


Architecture of the RS485 network

●Pear to pear

● bus


Optical network architecture

● pear to pear

● star

● daisy chain


Modbus protocol

Characterization of exchangesModbus protocol may be used to read or write one or more bits, one or more words, the content of the event counter or the contents of the diagnosis counters.

functions available:● reading of n output or internal bits,● reading of n input bits,● reading of n output or internal words,

● reading of n input words,

● writing of 1 bit,

● writing of 1 word,

● fast reading of 8 bits,

● diagnosis of exchanges,

● reading of event counter,

● writing of n bits,

● writing of n words.

master master

slave slave slave slave slave slave

request broadcasting

reply


- for PLC communication

●Created in 1979 by Modicon

Maximum number of slaves: 31

●For RS 485 or RS 232, and other links…

●Half-duplex protocol: one "speaker" at a time

●Master-slaves● query / reply

● broadcasting with no feedback

DATA LINKLAYER

2

NETWORK LAYER

3

TRANSPORTLAYER

4

SESSIONLAYER 5

APPLICATIONLAYER 7

PHYSICAL LAYER

1



RTU (Remote Terminal Unit) Modbus

Address CRC CheckDataFunctionsilence silence

- structure of a Modbus frame

● ASCII (American Standard Code of Information Interchange) ModbusAddress LRC CheckDataFunction: CR LF

3A Hex 0D Hex 0A Hex

Tolerance of one second silence between characters

Used more since faster

Silence >= 3.5 characters


N bytes 2 bytes 1 byte

Presentation of request and reply frames

RequestThe code is used to select the available requests

data required for the request, bit or word addresses,bit or word values,number of bits or words

when the message is received by the slave, the slave reads the check word and accepts or refuses the message

1 byte 1 byte N bytes 2 bytes

0 to FFhfunctioncode

data CRC 16

Reply

addresses of bits or words read, value of bits or words read, number of bits or words

0 to FFhfunctioncode

data CRC 16

1 byte

question

Tr < 10 ms reply

The time is given with the following parameters:

● 9600 bauds,

● 8-bit format, odd parity, 1 stop bit.


Modbus protocol: transmission medium occupancy diagram

request

answer

request

answer

to slave 1 to slave N

Analyse and answer

master

slave 1

slave N

physicalmedium

simultaneous execution of the order by all the slaves

analyse and next exchange

wait wait

exchangei - 1

exchangei + 1

broadcasting

exchangei

time

wait


Diagnosis counters

Sepam manages the following diagnosis counters:

● CPT1, first word: number of correct frames received, whether or not the slave is concerned,

● CPT2, second word: number of frames received with CRC errors, or frames received that are greater than 255 bytes and not interpreted, or frames received with at least one character that has a parity error, “overrun”, “framing”, “break” on the line. An incorrect rate causes incrementation of CPT2,

● CPT3, third word: number of exception replies generated (even if not sent, as result of a broadcast request),

● CPT4, fourth word: number of frames specifically addressed to the station (excluding broadcasting),

● CPT5, fifth word: number of broadcast frames received with no errors,

● CPT6, sixth word: not significant,

● CPT7, seventh word: number of “Sepam 2000 not ready” replies generated,

● CPT8, eighth word: number of frames received with at least one character that has a parity error, “overrun”, “framing”, “break” on the line,

● CPT9, ninth word: number of correct requests received and correctly executed.

The counters may be accessed via the dedicated reading function (see Modbus protocol function 11 in appendix).


Read function


Modbus address table in Sepam series 20


Format 16NS and 16S


Format B


Format X


TS remote annunciation list


Write function


Remote control order


Time-sequencing

A date is associated to each event:

● change of status of logic inputs

● change of status of automation data TS

● Internal data necessary for time-sequencing, time-setting, synchronization…

Internal clock in Sepam: year, month, day, hour, minute and milliseconds (0 to 59999).


Time-sequencing, synchronization

Input I21, 10 to 60 s synchronization signal.

Scada

Sepam

Sepam

Modbusnetwork

clock

Sepam

Sepam

Synchronization link

Modbusnetwork

scada

“External synchronization” via a logic input architecture “Internal synchronization via the comunication network” architecture

time-setting

4 words

message

10 s 20 s 30 s

∆ = ± 4 s


Exchange Principle

Request Zone

Reply Zone

Master

4events

3-Acknowledgement

1-Request

2-Reading

Status Change64 events

Storage zone


Exchange principle

Master 1

Acknowledgment

Reading

Master 2

Acknowledgment

Reading

64 eventzone

Inside SepamExchange word

4 e

v en

t zo

ne

4

ev e

nt

zon

e

4

0

Exchange word8

0

64 eventzone

Inside Sepam


Time-sequencingExchange table

exchangenumber

number of events

pollingword

event 1

event 2

event 3

event 4

incrementedupon each exchange

0 = empty tablex = x events4 maximum

1/reading if ≠ 0 in the event table2/writing to 0 for the following exchange

type of channel: 0 for input/800 for others

modbus data address

reserved: Ø

data status 0/1

not used year

month day

hour minutes

milliseconds 0 to 599998

mot

sMax. stock: 64 events.


Remote reading and remote setting

Protection and parameter settings available

• Setting of protection functions

• Sepam general characteristics


Reading of the settingsExchange principle

Request Zone

Reply Zone

Master

1-Request

2-Reading

Protection setting zone

50/51 overccurrent

50N/51N eath fault

27 under volltage


Remote parameter reading function

Request frameThe request is made by the supervisor, by means of a modbus "write words" command (code 6 or 16) at the address D080h of a 1-word frame which consists of the following:

D080h

function code

B15 B14 B13 B12 B11 B10 B09 B08 B07 B06 B05 B04 B03 B02 B01 B00

unit number

Reply frameThe reply sent back by Sepam is contained in a zone with a maximum length

of 125 words at the address D000h, which consists of the following: D00h

function code


unit numbersettings

…………

(specific fields for each function)

…………


Protection function parameters


Data Format


Remote settingsExchangePrinciple

Writing zone

Reply zone

Master

1-Writing request

3-check

Protection setting zone

50/51 overccurrent

50N/51N eath fault

27 under volltage

2- reading request


Remote reading of settings

function code = 01


unit number = 01type of curve = 00 00 (most significant)

type of curve = 00 00 (constant itme)

set point = 00 00 (most significant)

set point = 00 64 (set point at 100 A)

time delay = 00 00 (most significant)

time delay = 00 0A (time delay set to 10 x 10 = 100 ms)

00 00 (most significant)

00 00 (following values not significant, initalized to 0)

Data formatAll the settings are transmitted in the form of signed 32-bit integers (encoded, as a complement of 2).

Particular setting valuesA value equal to 7FFF FFFFh means that the setting is out of its validity range.

To inhibit a protection function, simply set the inhibition parameter to 8000 0000h, the other parameters stay the same. If all the setting values are read as 8000 0000h, it means that the protection function concerned is inhibited.


Disturbance recording

PresentationDisturbance recording is used to store analog and logical values.Sepam records a maximum of two disturbance records.Each record contains two files:

configuration file with suffix .CFG,data file with suffix .DAT.

The files are read by the supervision system via the Jbus link.A record may be transferred until it is overwritten by a new record.


Disturbance recordsExchange principle

Request zone

Aswer zone

Master

4-Acknoledgement

1-reading of available OPG

3-reading

EventsDisturbance 19 files max. *.cfg *.dat

Record zone

125 words

2-request

Identification zone

3-reading3-reading4-Acknoledgement


Communication diagnostics help (Modbus)

Check list

3) Asynchronous link (RS485)- Is the 2-wire/4-wire configuration correctly taken into account?- Are the L+ and L- connections OK (not inverted)?- Is the line polarised at the interface level (470 )?- Does the line have terminating resistors at each end (120 )?- Is the network length within the prescribed limit (EMC requirements)?

4) Connected products- Are the frames received and sent compatible with the functions supported by the supervision system and the products?- Are parameters correctly set (Baud rate, address, 2-wire/4-wire, etc.)?- Check on frame transmission and reception (control LED on modules).- Consistency of module addressing?

modbus communication

Documents

wayschneider electric

rs485 schneider electric

sepam connection

type of sepam

sepam series

remote annunciation

communication format

reactive power