Siemens PLC Communication Mastery: The Ultimate Guide to GET/PUT Instructions (Including Multi-Data Type Interaction)

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In industrial automation systems,real-time data interaction between multiple Siemens PLCs is key to achieving intelligent control. This article will delve into the configuration steps of GET/PUT instructions and demonstrate the cross-PLC interaction ofBoolean, Integer, Real, and String data types through complete SCL code.

1. Five Steps to Implement GET/PUT Communication

1. Establish Connection Configuration

• Add all PLC stations in the TIA Portal project

• Connect PLCs in the network view (no connection parameters need to be set)

• Set a fixed IP address for each PLC

Create Shared Data Block

• Create DB100 on the server-side PLC (disable “Optimize Block Access”)

• Define multi-data type variables:

  VAR

  Start_Flag : Bool; // Boolean

  Counter : Int; // Integer

  Temperature : Real; // Real

  Status_Text : String[10]; // String

  END_VAR

  

Configure Connection Parameters

• Create a new S7 connection in the “Connections” of the client PLC

• Select the partner PLC as the server

• Record the automatically generated connection ID (e.g., 0x00000001)

Write Client Program

• Use GET to read remote data

• Use PUT to write local data

• Handle communication status flags

Verify Communication Status

• Monitor communication status bits (DONE/ERROR)

• View data block changes online

• Use diagnostic buffer to troubleshoot errors

2. SCL Example of Multi-Data Type Interaction

Server-side PLC (Data Provider)

// Data block DB100 (disable optimized access)

DATA_BLOCK “ServerData”

VAR

// Address mapping: starts at 0.0

Start_Flag : BOOL := FALSE; // Address 0.0 (1 byte)

Counter : INT := 0; // Address 1.0 (2 bytes)

Temperature : REAL := 0.0; // Address 3.0 (4 bytes)

Status_Text : STRING[10] := ‘Ready’; // Address 7.0 (12 bytes)

END_VAR

Client-side PLC (Data Exchange End)

// Data block DB200 (local buffer)

DATA_BLOCK “ClientBuffer”

VAR

// GET read buffer

Read_Start : BOOL;

Read_Counter : INT;

Read_Temp : REAL;

Read_Status : STRING[10];

// PUT write data area

Write_Start : BOOL := TRUE;

Write_Counter : INT := 100;

Write_Temp : REAL := 25.5;

Write_Status : STRING[10] := ‘Running’;

// Communication status

GetDone : BOOL;

PutDone : BOOL;

GetError: BOOL;

PutError: BOOL;

StatusCode: INT;

END_VAR

// Communication program (called in cyclic interrupt OB)

VAR_TEMP

GetREQ : BOOL;

PutREQ : BOOL;

END_VAR

// Trigger command (1Hz pulse)

GetREQ := “Clock_1Hz”.Q;

PutREQ := “Clock_1Hz”.Q;

// Read server data

GET(

REQ := GetREQ,

ID := W#16#1, // Connection ID

ADDR_1 := P#DB100.DBX0.0 BYTE 19, // Read entire structure

RD_1 := P#DB200.DBX0.0 BYTE 19, // Store in read area

DONE => “ClientBuffer”.GetDone,

ERROR => “ClientBuffer”.GetError,

STATUS => “ClientBuffer”.StatusCode

);

// Write data to server

PUT(

REQ := PutREQ,

ID := W#16#2, // Another connection ID

ADDR_1 := P#DB100.DBX0.0 BYTE 19, // Server address

SD_1 := P#DB200.DBX10.0 BYTE 19, // Local write area

DONE => “ClientBuffer”.PutDone,

ERROR => “ClientBuffer”.PutError,

STATUS => “ClientBuffer”.StatusCode

);

// Data processing example

IF “ClientBuffer”.GetDone THEN

// Reset counter when receiving start signal

IF “ClientBuffer”.Read_Start THEN

“ClientBuffer”.Write_Counter := 0;

END_IF;

// Update status text when temperature is too high

IF “ClientBuffer”.Read_Temp > 50.0 THEN

“ClientBuffer”.Write_Status := ‘Overheat!’;

END_IF;

END_IF;

3. Key Points for Multi-Data Type Processing

String Processing Tips:

• Use<span><span>STRING[length]</span></span> to define explicitly

• Reserve 2 bytes for length information header

• Maximum length should not exceed 254 characters

4. Communication Status Diagnosis and Debugging

1. Status Code Analysis:

   CASE StatusCode OF

   0: // Success

   16#7002: // Invalid connection ID

   16#7005: // Data length exceeds limit

   16#80A2: // Remote object does not exist

   END_CASE;

2. Real-time Monitoring Tips:

• Use the “Communication Status” panel to view active connections

• Check data traffic in “Online and Diagnostics”

• Enable “Force Monitoring” to view data changes in real-time

Common Troubleshooting:

1. Connection failure → Check firewall settings and IP connectivity

2. Data misalignment → Ensure both sides have identical data block structures

3. Invalid write → Check the “write protection” status of the server DB

4. String truncation → Verify that length definitions match

5. Advanced Application Techniques

1. Data Packaging Optimization:

   // Use structures to encapsulate data

   TYPE “ProcessData” :

   STRUCT

   StartCmd : BOOL;

   Counter : INT;

   TempSet : REAL;

   Msg : STRING[10];

   END_STRUCT;

   END_TYPE

2. Timed Polling Strategy:

   // Different data uses different update frequencies

   IF “FastCycle”.Q THEN GET(…, ADDR_1:=P#DB100.DBX0.0 BYTE 3);

   IF “SlowCycle”.Q THEN GET(…, ADDR_1:=P#DB100.DBX3.0 BYTE 16);

3. Data Verification Mechanism:

   // Add CRC check bits

   “ClientBuffer”.Write_CRC := CALCULATE_CRC(

   ADDR := P#DB200.DBX10.0 BYTE 18,

   LEN := 18

   );

GET/PUT instructions are an economical and efficient solution for communication between Siemens PLCs. Through the SCL examples in this article, you have mastered the core technology of multi-data type interaction. In practical applications, it is recommended to:

1. Add verification mechanisms for important data

2. Use independent BOOL variables for critical control signals

3. Transfer large volumes of data in batches

4. Shorten polling cycles for data with high real-time requirements

#Industrial Automation #PLC Programming #Siemens SCL #Industrial Communication #Smart Manufacturing

If you want to learn Siemens SCL programming, you can purchase the first book below; if you want to learn ladder diagrams, you can buy the second book, which has detailed examples from basics to advanced.

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