Integrating SIMATIC RF685R UHF Readers into PCS 7 Using the Ident Library

In SIMATIC PCS 7 V9.0 SP1, integrating the SIMATIC RF685R UHF RFID reader (6GT2811-6BC10-0AA0) over PROFINET IO for multi-tag tracking requires deploying the specialized SIMATIC Ident Library for PCS 7 rather than raw communication drivers. For reliable multi-tag operations, engineers should utilize standardized higher-level technological blocks: Reset_Reader (FB1900) to initialize antenna power and carrier frequencies, Inventory (FB1901) to scan the radio frequency field and acquire all present Electronic Product Code (EPC-ID) transponders, and Read (FB1902) to sequentially extract memory payloads from specific tags. Avoiding the low-level Ident_Profile block ensures robust state-machine coordination and simplifies diagnostic alarm integration in Continuous Function Charts (CFC).

SIMATIC RF685R Architecture and PROFINET Integration in PCS 7

The SIMATIC RF685R (6GT2811-6BC10-0AA0) is an integrated high-frequency UHF RFID reader operating in the 865 to 868 MHz band (ETSI) and 902 to 928 MHz band (FCC). Featuring an integrated adaptive polarizing antenna and dual-port PROFINET IO interface, it is engineered for tracking material pallets, chemical drums, and container totes across process industries.

In SIMATIC PCS 7 V9.0 SP1, the RF685R connects as a standard distributed PROFINET IO device to an S7-400 or S7-410 controller. The device profile is defined in HW Config using its GSDML file. Data exchange occurs through standardized acyclic and cyclic PROFINET communication channels (submodule Ident Profile 4 Word or 32 Word), transferring RF command telegrams, transponder EPC-IDs, and diagnostic error codes directly into the controller memory.

Ident Library Structure: High-Level Blocks vs. Ident_Profile

When implementing RFID communication in Continuous Function Charts (CFC), engineers must choose between two programming methods:

The Raw Ident_Profile Block (Discouraged for Applications): The Ident_Profile block is a low-level communication driver that executes complex hex-formatted command strings. Managing multi-tag inventories, chaining read requests, and handling transponder collision arbitration manually in CFC logic requires extensive custom SCL/CFC state machines and is prone to buffer overflow faults.
Standard Modular Ident Blocks (Recommended): Siemens delivers pre-engineered, modular technological function blocks that wrap the Ident_Profile driver into simple command-response operations:
- Reset_Reader: Initializes the reader, configures antenna polarization, and resets RF channel errors.
- Inventory: Executes an RF sweep, arbitrating multiple UHF tags present in the antenna cone and outputting an array of detected EPC-IDs and Received Signal Strength Indicators (RSSI).
- Read: Takes a specific EPC-ID captured during inventory and extracts user data words from transponder memory banks.
- Write: Commits recipe or lot data to specific transponder memory.

Ident Function Block Portfolio and Execution Sequence Matrix

The following table summarizes the core Ident Library function blocks, their block numbers, and execution roles:

Block NameBlock NumberPrimary FunctionKey Input ParametersKey Output ParametersReset_ReaderFB1900 / FB45Initializes reader hardware & RF parametersEXECUTE, ADDR_OFFSET, CONF_DATADONE, BUSY, ERROR, STATUSInventoryFB1901Scans antenna cone for UHF transpondersEXECUTE, MODE (Continuous/Single)DONE, COUNT, EPC_LIST, RSSIReadFB1902Reads user data from designated transponderEXECUTE, EPC_ID, MEM_BANK, LENDONE, BUFFER, ERRORWriteFB1903Writes data payload to transponder memoryEXECUTE, EPC_ID, DATA_PTR, LENDONE, ERROR, STATUSIdent_ProfileFB1904 / FB101Low-level communication driver coreManaged internally by helper FBsInternal communication state

Step-by-Step Procedure to Configure RF685R Multi-Tag Reading

To configure the RF685R reader and execute automated multi-tag reading in PCS 7:

Configure Hardware in HW Config:
- Install the GSDML file for SIMATIC RF600 from the Siemens support portal.
- In HW Config, drag the SIMATIC RF685R onto the PROFINET IO branch of your S7-400 CPU.
- In the module sub-slots, insert the module Ident Profile (4 words or 32 words).
- Record the assigned input and output base addresses (e.g., 256).
- Save, compile, and download the hardware configuration to the controller.
Import Ident Library Blocks into Master Data Library:
- Open the SIMATIC Ident Library for PCS 7 in SIMATIC Manager.
- Copy blocks Reset_Reader, Inventory, Read, Write, and supporting UDTs into your Master Data Library.
- Synchronize block types across the multiproject.
Construct Technological State Machine in CFC:
- In a technological CFC chart (e.g., Pallet_Tracking), instantiate Reset_Reader.
- Connect the hardware base address (16#100 for address 256) to parameter HW_ADDR.
- Trigger Reset_Reader.EXECUTE on CPU startup (OB100) or via an operator initialization button.
- When Reset_Reader.DONE goes TRUE, enable Inventory.EXECUTE.
- When Inventory.DONE goes TRUE, read output COUNT (number of tags present in RF cone) and the array of EPC-IDs.
- Loop through the detected EPC-IDs using Read: connect the target EPC-ID to Read.EPC_ID, specify memory bank (3 for User Memory), and trigger Read.EXECUTE.
- Map the resulting data buffer to recipe tracking or plant batch parameters.
Compile and Download Changes:
- In CFC, execute Chart -> Compile -> Changes Only.
- Download changes to the S7-400 controller.

Verification

Verify RFID reading and multi-tag acquisition:
1. Place two UHF RFID transponders (e.g., SIMATIC RF640T) in front of the RF685R antenna.
2. In CFC online test mode, observe Inventory: confirm that output COUNT = 2 and that EPC_LIST[1] and EPC_LIST[2] populate with unique hex identifiers.
3. Confirm that the sequential Read execution sets DONE = 1 for each tag and extracts the programmed payload without communication errors (STATUS = 16#0000).
4. Verify that the RF685R front panel LED illuminates green (RF active) and flashes blue during data transmission.

Limitations and Operational Precautions

Metal and Liquid Interference: UHF radio waves reflect off metallic surfaces and attenuate in water. Position antennas with clear line-of-sight and avoid placing tags directly against bare metal without standoff spacers.
Antenna Cone Overlap: When deploying multiple RF685R readers in close proximity, configure dense-reader mode or alternate frequency channels to prevent RF cross-talk.
Commercial Accuracy Notice: Sizing and ordering RF685R readers (6GT2811-6BC10-0AA0) and transponders should be validated against official Siemens RFID product selection guides.

Engineer FAQ

Can I use the standard Ident_Profile block for RF685R in PCS 7?

While possible, it is strongly discouraged. Using high-level blocks (Reset_Reader, Inventory, Read) eliminates hundreds of lines of complex state-machine code.

How does the RF685R handle multiple tags simultaneously?

The reader executes an inventory sweep using anti-collision protocols (ISO 18000-6C / EPC Class 1 Gen 2), returning all tag EPC-IDs in a single array.

What memory banks are available on UHF transponders?

UHF tags feature four banks: Bank 0 (Reserved for kill/access passwords), Bank 1 (EPC Memory), Bank 2 (TID / Manufacturer ID), and Bank 3 (User Data Memory).