Overview
The Sinumerik 840D SL NCU 720.3B PN integrates a SIMATIC S7-300F-class central processing unit identified in the field as the CPU 317F-3 PN/DP. The integrated module carries the Sinumerik-specific material number 6FC5317-2FK14-0ABx and is electrically and functionally equivalent to the catalog S7-300F CPU 6ES7317-2FK14-0AB0. Engineers commissioning or maintaining a SINUMERIK 840D SL often cannot locate data sheets, manuals, or spare-parts entries for the 6FC5... article number in the standard Siemens Industry Mall product search because that MLFB belongs to the SINUMERIK product tree, not the SIMATIC catalog.
This reference documents:
- How to decode the CPU order designation and the embedded MLFB.
- The function of the three integrated interfaces.
- The fail-safe (F) capability of the module and the safety functions supported.
- Where to obtain official Siemens documentation, including the Distributed Safety and Safety Advanced manuals.
- Programming, configuration, and verification workflow in STEP 7 V5.x and TIA Portal.
Identifying the Integrated CPU
The CPU mounted inside the NCU 720.3B PN is a SIMATIC S7-300F CPU in the form factor of the standard S7-300. Two article numbers are encountered in the field:
| MLFB / Article Number | Product Tree | Description |
|---|---|---|
6FC5317-2FK14-0ABx |
SINUMERIK 840D SL spare parts | Integrated PLC CPU delivered as part of the NCU 720.3B PN. The trailing suffix (x) varies by hardware revision and export variant. |
6ES7317-2FK14-0AB0 |
SIMATIC S7-300F catalog | Catalog S7-300F CPU 317F-3 PN/DP. Functionally identical to the integrated CPU; serves as the primary reference for manuals, firmware notes, and support packages. |
6FC5... article belongs to the SINUMERIK 840D SL NCU replacement-parts catalog. It does not appear in the SIMATIC product finder. To obtain documentation, search for the equivalent 6ES7 317-2FK14-0AB0 MLFB in the Siemens Industry Online Support portal, or open a Siemens support request quoting both article numbers.
Decoding the Order Designation
The designation CPU 317F-3 PN/DP follows the standard S7-300 naming convention:
| Field | Meaning |
|---|---|
CPU 317 |
S7-300 performance class. The 317 sits in the upper-mid range, with expanded work memory and bit/word instruction performance above the 315/316 series. |
F |
Fail-safe variant. The CPU executes standard and safety programs side-by-side and is certified for use in safety functions up to SIL 3 (IEC 61508) / PL e (ISO 13849-1). |
3 |
Number of integrated interfaces on the CPU module itself. |
PN |
One of the three interfaces is a PROFINET interface. |
DP |
One of the three interfaces is a PROFIBUS DP interface (MPI/PROFIBUS combined physical port). |
Integrated Interfaces
The CPU provides three physical/logical interfaces, each assigned to a fixed socket on the front panel:
| # | Interface Label | Physical Port | Protocol(s) | Default Use |
|---|---|---|---|---|
| 1 | MPI/DP | 9-pin Sub-D, X1 | MPI (default) or PROFIBUS DP (master/slave, selectable) | Engineering station, HMI, or DP master/slave. Switchable via hardware configuration. |
| 2 | DP | 9-pin Sub-D, X2 | PROFIBUS DP master/slave | Distributed I/O (ET 200M, ET 200S, etc.), SINUMERIK I/O modules, drives, PROFIsafe slaves on PROFIBUS. |
| 3 | PN | 2 × RJ45, X3 port 1 / X3 port 2 (integrated 2-port switch) | PROFINET IO controller / device, PROFINET CBA, PROFIsafe over PROFINET | PROFINET I/O, PROFINET-based HMI, PROFIsafe safety communication. |
The PROFINET interface is an integrated 2-port switch with its own MAC addresses. The switch supports PROFINET IO with real-time (RT) and isochronous real-time (IRT) classes where the application requires them. The PROFINET interface also supports the PROFIsafe safety profile (PN-based PROFIsafe, profile V2.4 / V2.6 depending on firmware).
Fail-Safe Capability
The F suffix identifies the CPU as a SIMATIC F-CPU. The fail-safe architecture combines a standard user program and a safety program in a single CPU. The safety program uses a different instruction set (F-add-on instructions prefixed with F_) and runs inside a dedicated F-runtime environment that monitors execution and consistency.
Certified safety properties (per the SIMATIC Safety manual set):
- Suitable for safety functions up to SIL 3 per IEC 61508.
- Suitable for safety functions up to PL e / Category 4 per ISO 13849-1.
- Safety communication via PROFIsafe on both PROFIBUS DP and PROFINET.
- Self-diagnostics covering CPU, memory, I/O, and timing, with a defined PROFIsafe watchdog.
The safety program is generated, compiled, and signed with the SIMATIC Safety option package. Two generations of the option package are in field use:
| Option Package | Host Engineering Tool | Safety Profile | Status |
|---|---|---|---|
| SIMATIC Distributed Safety V5.4 SP5 (and later) | STEP 7 V5.5 / V5.6 | PROFIsafe V2.4 on PROFIBUS and PROFINET | Mainstream legacy environment for S7-300F / S7-400F. |
| SIMATIC Safety Advanced (TIA Portal) | TIA Portal V14 SP1 and later (with S7-300F CPU support package) | PROFIsafe V2.4 / V2.6 (CPU/firmware dependent) | Newer environment, supports S7-300F with limitations. |
| S7-300F / Distributed Safety (legacy) | STEP 7 V5.3 / V5.4 | PROFIsafe V2.0 / V2.4 | Legacy projects; preserved on existing installations only. |
The F-CPU does not perform the safety function by itself. It is the engineering and runtime environment. The actual safety function (e.g., safe stop, safe velocity, safe position) is implemented in the F-logic using approved F-application blocks such as FDBACK, FESTOP, FSV, FSP (Sinumerik-specific safety blocks for 840D SL), and the standard F-library blocks shipped with the safety option.
Typical Safety Functions Inside the 840D SL
On the SINUMERIK 840D SL NCU 720.3B PN, the integrated 317F-3 PN/DP is responsible for executing the PLC-side portion of the machine safety functions. The most common integrated safety functions are:
| Safety Function | Typical Implementation | Relevant Standard |
|---|---|---|
| Safe Stop 1 (SS1) | F-block FESTOP drives STO via PROFIsafe to the SINAMICS drive line-up. |
IEC 61800-5-2 |
| Safe Stop 2 (SS2) | Deceleration monitored by F-blocks, transition to SOS. | IEC 61800-5-2 |
| Safe Operating Stop (SOS) | Holds drive under closed-loop position control; position monitored. | IEC 61800-5-2 |
| Safe Limited Speed (SLS) | F-block FSV or drive-side SLS, selected via PROFIsafe. |
IEC 61800-5-2 |
| Safe Door Locking | Safety I/O via ET 200S F-modules or ET 200SP F-modules, F-block FDBACK. |
ISO 13849-1 |
| Emergency Stop | Hard-wired safety chain combined with F-logic acknowledgement. | ISO 13850 |
Documentation Sources
Use the following official Siemens documentation as the primary reference. The catalog S7-300F CPU manual set is the authoritative source for the integrated 317F-3 PN/DP.
-
Siemens Industry Online Support (SIOS) – entry portal for product manuals, firmware, FAQs, and support requests. Search MLFB
6ES7317-2FK14-0AB0. - SIMATIC S7-300 CPU 317F-3 PN/DP Manual – module description, wiring, diagnostics, technical data.
- S7-300F / ET 200S Distributed Safety – Configuring and Programming – safety program generation, PROFIsafe parameter assignment, F-runtime behaviour.
- SIMATIC Safety - Configuring and Programming (Safety Advanced in TIA Portal) – reference for the TIA Portal option package.
- SINUMERIK 840D sl PLC Programming Manual – base PLC program structure, NCK-PLC interface, F-block library for the 840D SL.
- SINUMERIK 840D sl Safety Integrated Commissioning Manual – drives + PLC + HMI integration, acceptance test procedures.
If a search for 6FC5317-2FK14-0ABx returns no result, use the equivalent catalog MLFB 6ES7317-2FK14-0AB0. To obtain the SINUMERIK-specific spare-parts documentation, file a support request on SIOS quoting both article numbers and the NCU serial number.
Programming and Configuration Workflow
Use the following procedure to commission or re-commission the integrated F-CPU inside the NCU 720.3B PN. STEP 7 V5.6 with the Distributed Safety option is the most widely supported path for S7-300F in the 840D SL environment.
- Establish the engineering connection. Connect the programming device to the PROFINET interface of the NCU (X3 port 1 or 2) or to the MPI/DP interface (X1). Use TCP/IP for PROFINET and MPI/Profibus for the legacy interface. Confirm the IP address and subnet of the NCU (default PROFINET 192.168.214.1 for SINUMERIK).
-
Open or create the STEP 7 project. Insert an S7-300 station with the CPU
6ES7 317-2FK14-0AB0(V2.6 or later firmware). The hardware catalog entry lists the module as CPU 317F-3 PN/DP. - Configure interfaces. Assign PROFINET device name, IP address, and subnet mask. Enable PROFINET IO controller mode and configure the connected PROFINET devices (SINAMICS drives, ET 200 stations, HMI panels). Configure PROFIBUS DP for distributed I/O if used.
- Install the safety option package. Open SIMATIC Manager → Options → Safety, or in TIA Portal open the Safety Administration. Activate the F-CPU and assign the F-source address (F_destinations are assigned per PROFIsafe slave).
- Author the standard user program. Implement OB1 (main), OB35 (cyclic), OB40 (hardware interrupts), OB82/OB83/OB85/OB86 (diagnostics), OB100 (restart). Include the standard 840D SL base PLC program (supplied by Siemens as the toolbox).
-
Author the safety program. In a separate F-FB or F-FC, use the F-library blocks (e.g.,
FDBACK,FESTOP,FSV,FACK_OP,FROUTE, etc.) to implement the required safety functions. Compile with the safety option to produce the signed F-runtime container. - Configure PROFIsafe. For each PROFIsafe slave, assign the F-source address (CPU PROFINET/PROFIBUS interface), F-destination address, watchdog time, and iParameter set. Use the F-monitoring time values from the device manuals.
- Download to the CPU. Download the hardware configuration, the standard program, and the signed safety program. The safety program is loaded with the F-password; the password is defined in the Safety Administration.
- Accept the safety program. Run the safety acceptance test. Print and sign the acceptance report. Archive the F-program, the F-block consistency check report, and the PROFIsafe parameter report.
Verification and Diagnostics
After configuration, verify F-operation with the following checks:
| Check | Method | Pass Criterion |
|---|---|---|
| CPU diagnostics buffer | STEP 7 → CPU → Module Information → Diagnostic Buffer | No F-stop errors; safety mode active. |
| Safety mode status | Online → F-CPU → Safety Mode | Mode = Safety mode active. |
| F-signature of safety program | Online → F-CPU → F-Signature | Signature matches the offline compiled value; signature is current. |
| PROFIsafe communication | Online → PROFIsafe diagnostics | All configured PROFIsafe slaves report OK; no CRC or sequence errors. |
| F-I/O passivation | Online → F-I/O → Status | All F-I/O channels in OK state; no passivated channels. |
| F-runtime container | Online → F-CPU → F-Container | Container loaded, CRC matches. |
| Standard user program | Online → Program Status | OB1/OB35 cyclic execution, no SF (system fault) LED. |
LED indicators on the integrated CPU faceplate inside the NCU 720.3B PN follow the standard S7-300F mapping:
- SF (red) – group error; check the diagnostic buffer.
- BF (red) – bus fault on the corresponding interface.
- DC5V (green) – internal 5 V supply OK.
- FRCE (yellow) – force operation active.
- RUN (green, flashing / steady) – CPU in startup or RUN.
- STOP (yellow) – CPU in STOP.
Troubleshooting Matrix
| Symptom | Probable Cause | Action |
|---|---|---|
No product search result for 6FC5317-2FK14-0ABx
|
Article belongs to SINUMERIK spare parts, not the SIMATIC catalog | Search 6ES7317-2FK14-0AB0 on SIOS or open a Siemens support request. |
| CPU goes to STOP after safety program download | F-signature mismatch or F-password mismatch | Recompile the safety program, re-enter the F-password, re-download. |
| PROFIsafe slave reports CRC error | F-monitoring time too short, or PROFIsafe address wrong | Increase F-watchdog per device manual; verify F-source/destination address pairs. |
| F-I/O channel passivated | Discrepancy time exceeded or short circuit on the safety I/O | Check the wiring, restart the channel, or re-accept if the cause was transient. |
| SF LED on, diagnostic buffer shows 'F-STOP' | F-runtime detected a logic error or program signature mismatch | Read the F-diagnostic buffer; correct the F-logic and re-compile. |
| PROFINET connection drops after PLC restart | PROFINET device name not retained on the device | Re-assign the PROFINET device name via the topology editor or the PRONETA tool. |
| Cannot install the safety option package | STEP 7/TIA Portal version mismatch | Use the compatibility matrix in the SIMATIC Safety manual to align tool version with the CPU firmware. |
Firmware and Compatibility Notes
Match the firmware of the integrated 317F-3 PN/DP against the engineering tool and the safety option package. Mismatched firmware causes F-signature failures and forces the F-CPU into STOP.
| CPU Firmware | Recommended Engineering Tool | Safety Option | Notes |
|---|---|---|---|
| V2.6.x | STEP 7 V5.5 SP2 / V5.6 | Distributed Safety V5.4 SP5+ | Widely deployed in 840D SL field population. |
| V3.2.x / V3.3.x | STEP 7 V5.6 or TIA Portal V15.1 + S7-300F support | Distributed Safety or Safety Advanced | PROFIsafe V2.6 support, expanded diagnostic buffer. |
| V3.4.x and later | TIA Portal V16 / V17 with S7-300F support | Safety Advanced | Latest 840D SL releases; verify SINUMERIK toolbox compatibility. |
Firmware updates for the integrated CPU are released by Siemens as SINUMERIK NCU firmware packages. The update procedure is described in the SINUMERIK 840D sl Commissioning Manual and uses the SINUMERIK boot screen or the SIMATIC Automation Tool. Firmware updates cannot be performed in RUN; the CPU must be in STOP or the NCU must be in the appropriate service state.
Spare-Parts and Service Notes
The integrated 317F-3 PN/DP is not field-replaceable as a standalone S7-300 module; it is part of the NCU 720.3B PN assembly. If the CPU is defective, the complete NCU is typically replaced. When ordering a spare, use the SINUMERIK MLFB 6FC5317-2FK14-0ABx. Before replacement, capture the project, the F-source address, the PROFIsafe parameters, and the safety program archive so they can be reloaded onto the new NCU.
When migrating from a non-F to an F CPU or from one firmware version to another, perform a complete safety re-acceptance test. The previous safety acceptance report does not cover the new configuration.
What does the 'F' in CPU 317F-3 PN/DP mean?
The 'F' identifies the CPU as a SIMATIC fail-safe F-CPU. It executes a standard user program and a signed safety program in parallel and is certified for safety functions up to SIL 3 (IEC 61508) and PL e / Category 4 (ISO 13849-1) when used with the SIMATIC Distributed Safety or SIMATIC Safety Advanced option package.
What does the '3' in the CPU 317F-3 PN/DP name mean?
The '3' indicates the number of integrated interfaces on the CPU module: (1) MPI/DP, (2) PROFIBUS DP, and (3) PROFINET (with integrated 2-port switch). Each interface is mapped to a fixed front-panel connector (X1, X2, X3).
Why does the article number 6FC5317-2FK14-0ABx not appear in the Siemens product search?
It belongs to the SINUMERIK 840D SL spare-parts catalog, not the SIMATIC catalog. The functionally equivalent catalog S7-300F CPU is 6ES7317-2FK14-0AB0. Search the Siemens Industry Online Support portal with this 6ES7 MLFB, or open a support request quoting both article numbers to obtain the SINUMERIK-specific documentation.
Which engineering tool and safety option package are required to program the integrated F-CPU?
STEP 7 V5.5 SP2 / V5.6 with the SIMATIC Distributed Safety V5.4 SP5 option package is the standard path for S7-300F in the 840D SL environment. TIA Portal V15.1 or later with SIMATIC Safety Advanced can also be used where the SINUMERIK toolbox supports it. Always match the CPU firmware against the compatibility matrix in the SIMATIC Safety manual.
How do I verify that the safety program is active after download?
Open Online → F-CPU → Safety Mode in STEP 7 and confirm the status is 'Safety mode active'. Then read the F-signature, the PROFIsafe diagnostics (all slaves OK), and the F-I/O status (no passivated channels). Record the values in the safety acceptance report and archive the signed F-runtime container.