RF300 ASM475 Integration on S7-300 CPU315-2DP via PROFIBUS

Overview: RF300 RFID and the S7-300 CPU315-2DP

The SIMATIC RF300 RFID system from Siemens is typically integrated with a SIMATIC S7-300 controller through the ASM 475 communication module (Article No. 6GT2002-0HA10). The ASM 475 is a slot-format module that physically resembles a standard S7-300 I/O module and acts as the bus coupler between the RF300 SLG (read/write device) and the higher-level automation system.

A common point of confusion during initial commissioning is whether the ASM 475 requires a PROFIBUS network. It does not. The ASM 475 has two operating modes, and the choice between them changes the entire hardware and software configuration:

• Direct rack mounting (backplane bus mode): The ASM 475 is inserted into a free slot of the S7-300 central rack (or a connected IM 360/361 expansion rack) and is addressed over the S7-300 backplane bus. No PROFIBUS segment is required for the RFID subsystem itself.
• PROFIBUS DP mode (remote mode): The ASM 475 is operated behind an ET 200M head module (e.g., IM 153-1 or IM 153-2) on a PROFIBUS DP segment. This is required when the RFID station must be physically remote from the CPU or when more slot addresses are needed in a distributed topology.

Per the Siemens RF300 system manual, the ASM 475 is described as a "communication module with an integrated bus connection to automation systems such as SIMATIC, SIMOTION, or SINUMERIK" and is offered in PROFIBUS and PROFINET variants. The PROFIBUS variant (6GT2002-0HA10) is the focus of this article.

Prerequisites and Required Components

Before starting, confirm that the following hardware, software, and licensing items are available. Incomplete prerequisite stacks are the most common source of commissioning stalls with RF300.

CPU 315-2DP Interface Architecture: X1 vs X2

The CPU 315-2DP exposes two physical interfaces, and the engineering decision to use one or both of them for PROFIBUS DP is a frequent stumbling block.

• Interface X1 (MPI/DP): Factory default is MPI (up to 187.5 kbps). X1 can be reconfigured in HW Config as a PROFIBUS DP master, but doing so disables MPI on X1. This conversion is only possible on CPU 315-2DP variants that carry the "DP" suffix in their designation; the CPU 315-2 does not support DP on X1.
• Interface X2 (DP master): The dedicated DP master port. This is the port normally used for the field-level PROFIBUS network that runs the ET 200M, ET 200S, or remote ASM 475.

To reconfigure X1 from MPI to DP master in STEP 7 V5.5: open HW Config, double-click the CPU 315-2DP, select the Interface tab, choose PROFIBUS from the interface type dropdown, click Properties, and create a PROFIBUS subnet with the desired baud rate (1.5 Mbps is the typical field-level default). After the change, X1 will behave as a second DP master interface and X2 can be assigned a different subnet or remain unused.

Configuration Path A: ASM 475 in the S7-300 Central Rack (No PROFIBUS Needed)

Use this path when the RF300 station is physically close to the CPU and no additional DP slaves are required on a separate segment.

1. Open HW Config and place the CPU 315-2DP in slot 2 of rack 0.
2. Insert the ASM 475 in any free slot from 4 to 11. Slot 3 is reserved for the IM (if used).
3. The ASM 475 entry is found under PROFIBUS DP > Identification Systems > SIMATIC RF-MOBY > ASM 475. In backplane mode it is dragged from the catalog into the central rack frame, not onto a DP subnet.
4. Double-click the ASM 475 and assign the RF300 SLG port addresses (4 bytes input / 4 bytes output per channel). The default address range starts at the next free byte after the last digital I/O module.
5. Save and compile (Station > Save and Compile). Download the hardware configuration to the CPU.
6. In the user program, instantiate the Ident profile function blocks. With the SIMATIC Ident library, FB 45 ("Ident") is the standard call interface; it is invoked with parameters such as the slot address, command, transponder UID, and length.

A minimal call to read a transponder's UID looks like the following Structured Text skeleton:

// One-shot read of a 4-byte UID on channel 1
iCmdCode := 1;            // READ
iAddr    := 0;            // start at transponder address 0
iLen     := 4;            // 4 bytes
bExecute := TRUE;

// Inputs to FB45
iIdentAddr  := 256;       // ASM475 logical address (from HW Config)
// Outputs
bDone  := FB45.DONE;
wError := FB45.ERROR;
bBusy  := FB45.BUSY;

Configuration Path B: ASM 475 Behind an ET 200M on PROFIBUS DP

Use this path when the RFID station is remote from the CPU, when the central rack is full, or when the customer wants the ASM 475 to behave as a standard DP slave (GSD-based integration).

1. Open HW Config and add a PROFIBUS DP master system to the CPU 315-2DP on interface X2 (or X1 if reconfigured).
2. Insert an IM 153-1 (6ES7153-1AA03-0XB0) or IM 153-2 (6ES7153-2BA10-0XB0) on the DP master system. The IM 153-2 is preferred when diagnostics time-stamping is required.
3. Open the IM 153 rack and place the ASM 475 in a free slot of the ET 200M.
4. Set the PROFIBUS address of the IM 153 to a value in the DP range (1–125, address 0 is reserved for the master; address 126 is the default for ET 200M with rotary switch).
5. Configure the ASM 475 I/O addresses. In distributed mode these are mapped into the S7-300 I/O address space according to the slot order; typical default for the first ASM 475 in the first ET 200M is starting at PI/PQ 256.
6. Compile and download the station.
7. Use the same Ident profile FBs in the user program; the logical base address of the ASM 475 is what FB 45 references.

GSD File Installation for ASM 475

The ASM 475 ships in the STEP 7 hardware catalog, which is why many users do not realize a GSD exists. However, a GSD file (SIEM8170.GSD or its newer variants) is required when:

• The ASM 475 is to be integrated into a non-Siemens PROFIBUS master.
• STEP 7 is replaced by a third-party configuration tool (e.g., COM PROFIBUS for legacy migration or a vendor-neutral PLC).
• A GSD-based DP-V0 slot is preferred for cyclic I/O with reduced complexity.

Installation procedure in STEP 7 V5.5:

1. Download the GSD package from the Siemens Industry Online Support portal (entry ID 90469980 or the RF300 product page).
2. Close HW Config.
3. In SIMATIC Manager, choose Options > Install GSD File.
4. Browse to the extracted GSD directory and confirm. The new device appears under PROFIBUS DP > Additional Field Devices > Identification Systems.
5. Restart HW Config so the catalog refreshes.

PROFIBUS Network Topology and Bus Parameters

When the ASM 475 is used in remote mode, the PROFIBUS segment must obey RS-485 cable length limits. The maximum segment length depends on the baud rate:

Each segment must have terminating resistors enabled at exactly two points (the physical ends of the segment). For the CPU 315-2DP, the X2 port ships with the bus terminator disabled; it is activated by a slide switch on the CPU housing or via the PROFIBUS connector. Activating the terminator at a mid-line CPU is a frequent error that causes intermittent slave timeouts.

The spur cable from the ASM 475 SLG connector to the RF300 reader must be ordered by part number (e.g., 6GT2091-4xxxx for 2 m, 5 m, 10 m, 20 m, 50 m) and must not exceed the rated length printed on the cable label. Exceeding this length corrupts the air-interface protocol and produces CRC errors in FB 45 status word STATUS[3].

Commissioning Verification

After download, run a structured verification sequence before declaring the cell operational.

1. Bus check: In HW Config, right-click the PROFIBUS subnet and select PROFIBUS > Diagnose. All configured slaves must appear with a green status. Any yellow or red entry must be resolved before continuing.
2. Module status: Online > Monitor/Modify, view the diagnostic buffer of the CPU. Entry "Module OK" should be present for the ASM 475.
3. SLG presence test: Use the Ident library's STATUS command to poll the connected SLG. A non-zero STATUS[1] or STATUS[2] indicates a cable or antenna fault.
4. Transponder test: Place an MDS D100 within the read range and call the READ command. Confirm that the UID is returned and that ERROR = FALSE.
5. LED check: The ASM 475 front-panel LED should show steady green on SF and DP; the SLG should show green on the antenna LED when a transponder is in the field.

Troubleshooting Matrix

Notes on Migration to PROFINET

The PROFIBUS variant of the ASM 475 (6GT2002-0HA10) cannot be converted to PROFINET in the field. For new installations where PROFINET is preferred, Siemens offers the ASM 456 (6GT2002-0HA20) or the RF186C/RF188C communication modules, which are mechanically compatible with the S7-300 slot format but connect to a PROFINET segment via the backplane bus. When migrating an existing cell, leave the ASM 475 in service and add the ASM 456 as a parallel module if additional PROFINET readers are required; do not attempt to hot-swap a PROFIBUS module into a PROFINET topology.

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