Migrating Legacy SEND_R and REC_R Communication Blocks to Modern PCS 7 APL Blocks

In SIMATIC PCS 7 V8.0 and higher, the classic communication blocks SEND_R (FB209) and REC_R (FB210) from the PCS 7 Standard Library V7.1 were removed from the default Basis Library and moved to DVD 2 under Additional Products. To implement cross-controller S7 communication in modern PCS 7 projects, migrate to the native Advanced Process Library (APL) communication blocks Snd_AnaVal (FB1894) and Rcv_AnaVal (FB1895), or deploy standard S7 communication blocks BSEND (SFB12) and BRCV (SFB13) configured in NetPro.

Decoupling of the PCS 7 Standard Library and Transition to APL

In SIMATIC PCS 7 V7.1, automation engineers relied extensively on the PCS 7 Standard Library (often called the Classic or Standard Library), which included function blocks such as SEND_R (FB209) and REC_R (FB210) located in the COMM family for transmitting REAL process values over configured S7 connections.

Beginning with SIMATIC PCS 7 V8.0, Siemens transitioned entirely to the Advanced Process Library (APL). During this transition:
1. The classic PCS 7 Standard Library was decoupled from the primary installation image and placed onto DVD 2: Additional Products under the directory \Additional_Products\PCS7LIBRARY__V7.1+SP3.
2. The core system manuals (such as the PCS 7 Basis Library V8.0 Manual) continued to list SEND_R and REC_R in their appendix tables solely for resource load estimation (CPU scan time, work memory, and communication instances) to aid engineers migrating legacy projects.
3. Because the blocks are not installed in the default APL or Basis Library catalogs, searching for FB209 or FB210 in a fresh PCS 7 V8.0/V8.1 installation yields no results.

To maintain engineering consistency, plants must either install the legacy library package as an interim bridge or upgrade their cross-controller architectures to native APL communication blocks.

Cross-Controller Communication Block Selection Matrix

Evaluate available communication blocks for cross-controller data exchange in PCS 7:

Block NameBlock NumberLibrary OriginData Types SupportedNative Quality Code (ST) HandlingRecommended ApplicationSEND_R / REC_RFB209 / FB210Legacy PCS 7 Library V7.1REAL (up to 32 analog values)No (Raw REAL arrays only)Maintaining legacy S7-400 projects without re-engineeringSnd_AnaVal / Rcv_AnaValFB1894 / FB1895PCS 7 AP Library (APL) V8.1+REAL with APL StructureYes (Transfers Value + ST byte)Modern APL cross-AS analog telemetrySnd_DigVal / Rcv_DigValFB1896 / FB1897PCS 7 AP Library (APL) V8.1+BOOL with APL StructureYes (Transfers Value + ST byte)Modern APL cross-AS digital interlocksBSEND / BRCVSFB12 / SFB13S7 System Function BlockAny data structure (up to 64 KB)Manual byte packing requiredBulk recipe, table, or array data transfersUSEND / URCVSFB8 / SFB9S7 System Function BlockUncoordinated data transferManual byte packing requiredNon-critical high-frequency cyclic telemetry

Engineering notice: APL communication blocks preserve NAMUR NE 107 signal status bytes across network boundaries.

Installing Legacy Standard Library V7.1 from Additional Products Media

If legacy plant standards require retaining SEND_R and REC_R on PCS 7 V8.0 / V8.1:

Locate Installation Media:
* Insert or mount PCS 7 V8.0 / V8.1 DVD 2 (Additional Products).
* Navigate to the folder:
DVD_2\Additional_Products\PCS7LIBRARY__V7.1+SP3
Execute Library Setup:
* Right-click Setup.exe and select Run as Administrator.
* Follow the installation wizard to install the legacy blocks into STEP 7.
Open and Retrieve Blocks in SIMATIC Manager:
* In SIMATIC Manager, select File > Open > Libraries.
* Open PCS 7 Library V7.1.
* Locate the Blocks folder, find SEND_R (FB209) and REC_R (FB210), and copy them into your project's master data library.
* Update the CFC block catalog to instantiate them.

Migrating to Native APL Blocks (Snd_AnaVal / Rcv_AnaVal)

To upgrade to modern APL communication blocks in PCS 7 V8.1 and higher:

Configure S7 Connection in NetPro:
* Open NetPro.
* Create a bilateral S7 Connection between Controller A and Controller B.
* Note the local connection ID (e.g., W#16#0001).
* Download NetPro network configurations to both AS stations.
Instantiate APL Driver Blocks in CFC:
* In Controller A, insert Snd_AnaVal (FB1894) into a cyclic chart (OB 35).
* Parameterize ID with the NetPro connection handle.
* Connect process values (e.g., MonAnL.PV_Out) to inputs In01 through In16.
* In Controller B, insert Rcv_AnaVal (FB1895) with the matching connection ID.
* Connect outputs Out01 through Out16 directly to downstream interlocks or controllers.
Automatic Status Propagation:
* Unlike legacy SEND_R, Snd_AnaVal transmits both the floating-point value and the Signal Status (ST = 16#80, 16#60, 16#00). If Controller A's sensor fails, Controller B's faceplate immediately detects the bad quality code without requiring custom alarm bits.

Verification

Verify cross-controller communication:
1. Online in Controller A CFC: Force a test value (e.g., 45.67) on Snd_AnaVal.In01.Value.
2. Online in Controller B CFC: Confirm that Rcv_AnaVal.Out01.Value registers 45.67 within one communication cycle.
3. Disconnect the plant bus cable between the two controllers: Confirm that Rcv_AnaVal flags Error = 1 and sets signal status ST = 16#00 (Bad), causing downstream APL blocks to enter fail-safe substitute states.

Limitations and Operational Precautions

Legacy Standard Library V7.1 is not supported in PCS 7 V9.0 and higher; continuing to use FB209 and FB210 creates technical debt and prevents upgrading to CPU 410-5H firmware.
Ensure S7 connection quotas on S7-400 CPUs are not exceeded; each configured S7 connection consumes one connection resource handle.
Do not trigger BSEND or Snd_AnaVal in rapid OB 30 (10 ms) cycles without throttled send clocks, as this saturates the CP 443-1 communication buffer.

Engineer FAQ

Why did the PCS 7 Basis Library manual list SEND_R if the block was missing?

The Basis Library manual included SEND_R and REC_R in its resource consumption appendix to assist engineers migrating older V7.1 projects. The table documented memory footprints, not catalog inclusion.