Method for realizing MODBUS-RTU master station communication using CP341 in Siemens PCS7 system - Database & Sql Blog Articles

1:

Siemens

PCS7

System hardware configuration environment

,

Introduction to engineering examples

1) PLC

for

CPU414-5H

redundancy

PLC, CP341(

use

IM153-2), CP341

Main station hardware dog

Dongle ( 6ES7 870-1AA0-0YA0 )

2) CP341

Can be extended multiple

,

Currently used at most

10

One

CP341,

But need to pay attention to

CPU

In the attribute

Cycle/Clock Memory

Process image area

SIZE

by

"768"

Change to bigger

,

Such as

"1024"

2:

Siemens

PCS7

System software configuration environment

1) PCS7 V8.1

Siemens

PCS7

Programming configuration software

2) CP PtP Param V5.1 SP14

Serial communication module driver

3) CP PtP Modbus Master V3.1 SP7 CP341

of

Modbus

Master station driver protocol

,

Must be installed

CP PtP Param V5.1 SP14

Then install this driver

3: CP341

Hardware configuration

1)

Double click to open

CP341

Property dialog

,

Click

"Parameters"

Button

,

Then choose

"Modbus Master";

2)

Double click

Protocol ,

Setting

Modbus

Communication baud rate

,

Stop bit and parity bit

,

As shown

:

The parameter is set to

: 9600, 8-N-1,

Each slave must be consistent with this

;

3)

Setting the electrical interface

,

Choose to be half duplex

2

line

RS485,

The electrical interface standard of each slave must be consistent with the master station

;

4) Save after configuration is complete

,

And loading

,

Redundancy during loading

CPU

Must be set to

STOP

mode

.

4:

software programming

1)

First you need to manually set up the send and receive data blocks.

DB,

Open component view

,

in

Blocks

Established in

,

For example, the send data block is defined as

DB51,

And define the symbolic name

:SOURCE_DB (

This symbol name must be defined

),

Define after opening the data block

Modbus

Function code data format

,

As shown

: address

Slave address is

1

,

Code

Function code is

3

(Read holding register area as

40001/400001

),

Reg_startadr

The start address of the register is

0

,

Reg_count

Read

25

Register data, which can define multiple different slave addresses in this order

,

Different function codes, different registers.

2

) Define the receive data block

DB52

, the symbol name is:

DESTINATION_DB

It is used to store different data from the slave station. When the slave register address is programmed in the slave station, it is better to plan the data that needs to communicate with the master station to the continuous register area, and the data type is preferably kept consistent. If the address is not continuous, Or the data type is different, then you need to manually establish multiple receiving addresses here, as shown in the figure.

Receive1

Defined as an array containing

25

Real-type types, and registers that are not consecutively addressed and have different data types must be created manually.

3

) is different from

STEP7

Ladder programming

, PCS7

Used in

CFC

Programming, in the factory view,"

Device Information

Established

CFC

Communication program

"comm",

this

CFC

In the program

OB33

Use the loop mode to train each read function block, when the number is

1

Execution

CFC

Figure

2

The first block in , is

2

Execution chart

2

The second block in the program, and so on;

CFC

Figure

2

Transmitting block

FB8

(

P_SND_RK

)

The pin in the definition is as shown below.

LADDR

In the example

592

, refer to the third step

CP341

Hardware configuration;

DBB

_NO

In the example, the first sending block is

0

, the second sending block is

6

, the third sending block is

12

, here reference

DB51

Define the address of the part;

CFC

Figure

2

Medium receiving block

FB7

(

P_RCV_RK

)

The pin in the definition is as shown below.

LADDR

In the example

592

,

DB_NO

In the example

DB52

,

DBB

_NO

In the example, the first sending block is

0

, the second sending block is

100

, the third sending block is

158

, here reference

DB52

Define part of the address

5:

CP341

Troubleshooting

Fault diagnosis is divided into five methods

:

1)

by

CP341

of

led

Lamp for diagnosis

, SF (

red

)

An error has occurred

(

Such as hardware failure

,

Firmware error

,

Communication line between master and slave is disconnected

)

Or reassigning parameters

; TXD (

green

)

Lights up when sending data,

RXD (

green

)

Lights up when receiving data;

2)

by

FB7

with

FB8

Functional block

STATUS

The parameters are diagnosed, and the specific parameter values ​​represent the meanings of the Siemens related documents;

3)

by

CP341

Diagnostic buffer for diagnosis;

4)

Diagnostic interrupt indication

CP341

failure;

5)

Diagnose through the serial port debugging assistant.

6

:be careful:

1

) use of this

OB33

The communication program with timed interruption has drawbacks, which will prolong the communication time, which may cause packet loss and other phenomena. It needs to be modified to

OB1

Writing communication programs and using

FB8

of

DONE

with

ERROR

Bit activation receives the request and then uses

FB7

of

NDR

with

ERROR

Bit activation next

FB8

, and so on until the last one

FB8

After writing the program, you can pass the run group and the default

OB33

Communication program in

Comm

"Clip to

OB1

In, as shown below:

2

) After writing the program to download

CPU

After that, if it is modified

DB51

or

DB52

Related settings, need to

DB

Initialize, otherwise it will not be able to communicate, the steps are as follows:

turn on

DB

Piece

---

"

VIEW

”

---

by"

Declaration view

Switch

"

Data view

”

---

"

EDIT

”

---

"

Initialize Data Block

”

,

After the change, you need to check if the current data is the required data, and then download the program.

3

)

CP341

Communication

Just pick up

15

needle

D

Type connector

4

with

11

Pin, no need to short

2

with

4

Pin and

9

with

11

Pin. When the actual communication cable length is greater than

50

When using meters, add resistance to both ends of the bus.

330

Ohmic termination resistance. make sure

A

,

B

The correct connection of the signal lines.

4

)

CP341

If the data read is to be displayed on the screen, except

DB

Upload a small red flag to a single data in the block.

WINCC

Screen, you can also pass

APL

The library's program uploads the data to

WINCC

Screen, the panel generated in this way is more user-friendly, integrating various alarms, high and low limits, trends, etc.

The picture below will

CP341

After the data is normalized, upload it to

WINCC

And generate a unified panel