Simatic Modbus Training v2

5/28/2018 Simatic Modbus Training v2

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Modbus Slave&

Modbus Masterin S7

Refer to the Modbus Serial Pack v2 zip.

-Project Modbus v2

-Manuals for drivers and hardware


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Siemens AG 2008 - Subject to modifications

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Preparation..

To enable the Modbus functionality of the CP cards, you must do

three things:

1. Install Point to Point software from

http://support.automation.siemens.com/WW/view/en/27013524

2. Install Modbus Master and Slave drivers fromhttp://support.automation.siemens.com/WW/view/en/27774018

http://support.automation.siemens.com/WW/view/en/27774276

3. Fit the Modbus dongle to the rear of the CP

4. Install the driver to the CP

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http://support.automation.siemens.com/WW/view/en/27013524http://support.automation.siemens.com/WW/view/en/27774018http://support.automation.siemens.com/WW/view/en/27774276http://support.automation.siemens.com/WW/view/en/27774276http://support.automation.siemens.com/WW/view/en/27774018http://support.automation.siemens.com/WW/view/en/27013524


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Summary of the GOULD-MODBUS Protocol

The type of data exchange between MODBUS systems is controlled by

Function Codes (FCs).

The following FCs can be used to carry out data exchange bit-by-bit:

FC 01 Read coil (output) status,

FC 02 Read input status,

FC 05 Force single coil,

FC 15 Force multiple coils.

The following FCs can be used to carry out data exchange register-by-

register:FC 03 Read holding registers,

FC 04 Read input registers,

FC 06 Preset single register,

FC 16 Preset multiple registers.

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Summary of the GOULD-MODBUS Protocol

Function Code Modbus Address Range AccessOutput Coils

Function Codes 01, 05, 15

00001 - 09999 Read/Write

Input Coils

Function Code 02

10001 - 19999 Read Only

Internal RegistersFunction Code 04

30001 - 39999 Read Only

Holding Registers

Function Codes 03, 06, 16

40001 - 49999 Read/Write

It will save considerable time and frustration to have a good idea upfront of

the mapping of Modbus data to S7 data. The Modbus slave will define the

function codes to be used by virtue of the fact that specific data is held in

specific Modbus registers.

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Configure the Hardware as Modbus Slave

With the software installed you can now open the Hardware Configuration

and configure the CP341 in your rack. Double click the CP to open its

properties and click on the Parameter button. The Point to Point

configuration software will now open.

From the drop down box at the top left, select Modbus Slave as the

Protocol. Next double click the Protocol icon in the middle of the screen.

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Configure the Driver..

You are now presented with a number of tabs. The first tab "General" shows

the driver versions in use. This is for information only. The second tab

"Modbus-Slave" allows you to define the communications properties of the

system, baud, stop bits etc.

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On the tab labelled FC01, 05, 15, you can enter the Modbus address ranges

to be mapped into M area, Outputs, Timers and Counters. If any areas are

not used, enter 0.

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On the tab FC02, you can define the mapping for M area and Inputs to be

read from.

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On the tab FC03, 06, 16 you only need to enter a DB number. Thesefunction codes use the address range starting from Modbus address 40000.

The DB number specified is the start DB of a range of DB's that are

generated by the user and must be 512 words long. If your Modbus address

is say 40513, you would need to generate another consecutively numbered

DB of 512 words long. Modbus address 40513 would be the first address in

the second DB (word 0 of the second DB, the 513 word in total).

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The tab labelled FC4 is configured in the same way but for the 30000

address range.

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The next tab is labelled "Limits". This is where you can define the range ofDB's, Memory and Outputs to be written to by FC05, FC15, FC06 and

FC16. If you were to use the Modbus address 40513, this would reside in

the second DB at word 0. You would therefore need to set the limits here to

DB1 and DB2 (assuming DB1 is the DB selected for use by FC03, 06, 16).

This is similar for M and Q areas. The final tab defines any electrical

properties.

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Download Hardware Configuration and Modbus Driver..

Save and Compile the Hardware Configuration then download to the

controller. Once the configuration is downloaded we can install the driver to

the CP. To do this you must have an online connection and use the Load

Drivers button from the Driver Parameters (as we have just configured).

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Movement of Modbus Data between the CP to the User Program.

Now the driver is configured. It knows what to do when it receives a Modbus

telegramread or write data to or from a specific Simatic area. Now that

the Modbus data can be interpreted by the Modbus driver on the CP341, we

need to move the data from the CP to the CPU of the PLC. This is done by

use of FB80 MODB_341. This block can be found in the library entitled

"Modbus". The block is called as part of the cyclic user program via OB1. It

needs to know the logical address (LADDR) of the CP341 from thehardware configuration which can be found by highlighting the CP in the

rack in Hardware Configuration. The address will be shown under the I-

address column of the bottom half of the window.

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Block Dependencies:

When you add the FB80 block to the user program, you will be required to

generate an Instance Data Block. BEFOREgenerating this block, ensure

that the FB7 and FB8 blocks are also present in the blocks folder (these are

found in the same Modbus library). This is because FB80 uses these blocks

to communicate with the CP.

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OB100Startup OB

The only coding that the user must perform is in OB100, where we set a bit

on and a bit off to initialise the FB on start-up of the CPU, used at the

parameters CP_START and CP_START_FM.

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OB1Main Cyclic OB

Call FB80 in OB1 and assign addresses

for status reporting. Also assign the

CP_Start and CP_Start_FM bits

generated in OB100.

Download all program blocks to the

controller and test!!!

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Configure the Hardware as Modbus Master

To configure the Modbus Master, we start in Hardware Configuration.

Perform the same steps as for the slave (selecting Modbus Master as the

Protocol) and click on the Protocol icon in the middle of the screen.

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Here you have three tabs. The first, "General" identifies the driver version,

as in the slave. The second, "Modbus Master" is where you define the

communications properties, stop bits, baud etc.

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The final tab defines any electrical properties. This is the hardware

configured for operation. We must now send and receive data to/from the

CP341.

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OB1Main Cyclic OB

In the cyclic user program we must

call two blocks, P_SND_RK and

P_RCV_RK, found in the Modbus

library. The Modbus Master will send

a request for data to its slave

(reading values) or simply send it

data (writing).

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The send block is used to send a number of bytes that are structured in a

specific way and populated with specific data, depending upon the function

code to be used. For example, FC03 requires the first byte to contain the

slave address, the second byte to contain the function code number, the

third and fourth bytes (DBW2) must contain the Modbus start address and

bytes five and six (DBW4) contain a value representing the number of

registers required.

*(All of the structures of data for the various function codes can be found in section 5 of the Modbus master manual).

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OB1Main Cyclic OB

You will need to define a DB

that can be used to receive

the data into. You call the

receive block, and populateits parameters similarly to the

send block, telling it the

LADDR of the CP341 and the

DB to which the data is to be

received.

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With these blocks now configured, you can download to the

hardware and you should have a working Modbus master. Of

course, the blocks will need code writing around them for timing the

send and receives and also error handling, but I recommend using

a VAT (variable table) to manually trigger sends etc until you are

happy that the system is functioning. This way you are in control ofthe requests and also the data that is sent.

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S7-400 Modbus Master and Modbus Slave

The configuration is similar when using the S7-400. Differences include the

possibility to install two interface modules to one CP441-2, which can be

configured independently for different functions. These interface modules

are fitted to the front of the CP, with the type dependant upon the electrical

connection to the system (RS232, RS485, RS422). The driver configuration

is identical to when using the S7-300.

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There are differences in the blocks

used for both slave and master

functions in the S7-400.

Firstly, the slave uses block FB180

MODB_441. This can be found in the

same location as the block used in

the S7-300.

Secondly, the master uses different

blocks to the S7-300. The S7-400

uses the System Function Blocks

SFB12 and 13 (BSEND and BRCV).

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The main difference with both the master and slave blocks is the requirement of a

connection between the devices. This connection is configured in Netpro and the ID of

this connection is entered as a parameter to the send and receive blocks. The

connection type is Point to Point. Once a new connection of the type Point to Point is

added to the configuration, you can view the properties of it. Here you can set the CP to

be used and select which of the CPs interfaces are to be connected. You also find the

connection ID, whose value needs to be entered to the send and receive blocks.

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Diagnostics

Sometimes you may have configured the system but devices do not

communicate in the manner you expected. Things may appear to be healthy

but data is not being successfully transferred. If this is the case then you

have a number of options available.

The first place to check would be on the block calls. The blocks will generate

status and error information.

Secondly, you can check the Module Information of the CPU and CP for any

diagnostic entries.

Error codes generated on the block calls and in Module Information can be

found in the manuals included in the Modbus Serial Pack.

A further option is to monitor the network using a network analyzer. This will

enable you to see the raw data present on the network media and determine

if it is present and correct. You should be seeing telegrams with the format

matching that described in chapter 5 of the Modbus master manual,

depending upon the function code being implemented (byte 1 should

contain the slave address, byte 2 should contain the function code etc).

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Multipoint Connection Details..

In the RS422 mode CP341 and CP441-2 can only be used as a Master

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The following applies for both modules:

GND (PIN 8 by CP341 / CP441-2) must always be connected on

both sides

The casing shield must be installed everywhere

A terminating resistor of approx. 330 is to be soldered into the

connector on the last receiver of a node sequence

Recommended cable type: LIYCY 3 x 2 x 0,14 R(A)/R(B) andT(A)/T(B) twisted pairs

A wiring with Stub is not allowed

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Documents

Simatic Modbus Training v2