Migrating SIMATIC S5 to S7-300/400: IO Adapters, STEP 7 Tools

Overview: Why Migrate from SIMATIC S5 to S7

The SIMATIC S5 family (S5-90U, S5-95U, S5-100U, S5-115U, S5-130U, S5-135U, S5-155U, S5-155H) reached the end of its product life cycle. Spare parts availability is limited, repairs become cost-prohibitive, and many S5 CPUs (e.g., 6ES5 941, 6ES5 942, 6ES5 944, 6ES5 948) are no longer in serial production. The successor families S7-300 (6ES7 3xx modules), S7-400 (6ES7 4xx modules), and the current S7-1200/S7-1500 platforms provide a migration target. S7-300 and S7-400 are the most common drop-in replacement because they reuse the same 24 V DC I/O voltage levels and the same PROFIBUS-DP cable plant that was used in S5-115U/-135U/-155U networks.

Two distinct workstreams run in parallel during any S5 to S7 conversion:

1. Hardware conversion — replacing the S5 rack/CPU/IM with S7-300 or S7-400 hardware, ideally without re-stripping the field wiring.
2. Software conversion — translating S5 STL (Statement List), S5-CPU firmware blocks, S5 COM packages, and S5 data structures into STEP 7 STL/SCL/FBD for the S7 CPU.

Siemens publishes a consolidated entry point that gathers the conversion manuals, tools, spare-parts lists, COM packages, and adapter catalogs that are required for a full migration. The main portal entry is SIOS entry 16612444 — SIMATIC S5 to S7 migration. Two reference documents sit underneath that entry and are referenced throughout this article:

• STEP 7 — From S5 to S7 (PDF, document ID 1118413)
• SIMATIC S5 to S7 Migration / Renewal Manual

Migration Planning: Phased Approach and Scope Definition

A S5 to S7 migration is rarely a single cutover event. Plan it as a phased program and define the cutover criterion up front. A typical five-phase structure is recommended by the Siemens migration manual:

1. Inventory and assessment — list every S5 CPU, IM, and I/O module; record firmware versions, memory submodule contents, and the program blocks loaded in each CPU.
2. Target platform selection — S7-300 (CPU 31x, 6ES7 31x series) for mid-size machines, S7-400 (CPU 41x/416/417, 6ES7 41x series) for large process plants, S7-1500 (CPU 15xx, 6ES7 5xx series) for greenfield replacements that will eventually move to TIA Portal.
3. Hardware pilot — convert one rack or one machine first using the rewire-free adapter approach (see below).
4. Software conversion and FAT — translate S5 STL with the S5 to S7 conversion tool, perform I/O checkout, run the original HMI on the new S7 side, then sign off.
5. Production cutover — schedule a maintenance window; freeze S5 program changes; perform the swap; run IO check on every channel before powering the machine.

Two planning parameters must be locked in before the cutover:

• The address mapping between S5 byte addresses (I, Q, F, T, C, M, D) and S7 addresses (I, Q, M, DB, T, C). The STEP 7 — From S5 to S7 manual provides a default mapping table for direct conversion.
• The I/O channel count, which is the gating parameter for selecting the rewire-free adapter family (see next section).

Hardware Migration: Rewire-Free S5-to-S7 IO Adapters

The fastest hardware path is to keep the existing S5 front connectors and field wiring, and to use the Siemens S5-to-S7 adapter family to translate between the S5 front connector and the S7-300 or S7-400 module. The adapter catalog (S5 S7_Adapter_Eng_V3_0.PDF, distributed through the SIOS portal at SIOS entry 16612444) catalogs one adapter per S5 I/O module family and per S7 target module family.

Conceptually the adapter is a passive printed-circuit board (no firmware, no software, no DIP switch) that maps:

• S5-115U 6ES5 4xx digital input pinout → S7-300 SM 321 (6ES7 321-1Bxxx) digital input pinout.
• S5-115U 6ES5 4xx digital output pinout → S7-300 SM 322 (6ES7 322-1Bxxx) digital output pinout.
• S5-135U/155U 6ES5 6xx high-density digital input pinout → S7-400 SM 421 (6ES7 421-1Bxxx) digital input pinout.
• S5-115U analog input 6ES5 4xx-7xxxx / 6ES5 4xx-8xxxx → S7-300 SM 331 (6ES7 331-7Kxxx).
• S5-115U analog output 6ES5 4xx-5xxxx → S7-300 SM 332 (6ES7 332-5HDxx).

The S5 front connector stays on the field wires. The adapter is plugged between the S5 front connector and the S7 module header. No re-stripping of the field wires is required, which is the main reason the changeover time is dominated by program conversion and not wiring.

Adapters for S7-300 and S7-400: Mounting and Wiring

The mechanical integration differs between the two platforms because the S7-300 and S7-400 use different module formats.

S7-400 — direct plug-on

S7-400 digital and analog I/O modules (6ES7 421/422/431/432) use a front connector that is keyed and latched onto the module header. The S5-to-S7 adapter for the S7-400 plugs directly on top of the S7-400 module: the bottom of the adapter carries the S7-400 module's front-connector pin pattern, the top of the adapter carries the S5 front-connector pattern. The S5 front connector that is already wired to the field is then latched onto the adapter. The mechanical stack is therefore: DIN rail → S7-400 module → adapter → S5 front connector. Each adapter is a passive device sized to match the S7-400 module's footprint. No rack modification is required.

S7-300 — adapter rack

The S7-300 module format is different: the front connector latches directly onto the S7-300 module header and the module is mounted on a 35 mm DIN rail. The S5-to-S7 adapter for the S7-300 is therefore a small DIN-rail-mounted sub-rack that holds the S5 front connector at its original pitch and routes the pins onto a short S7-300 front connector that latches onto the S7-300 module. The field wires on the S5 front connector do not move. The S7-300 module is mounted on the same DIN rail, immediately to the left or right of the adapter sub-rack. The result is the same: zero re-wiring at the field end.

Mounting sequence on the S7-300 side:

1. Remove the S5-115U/-135U/-155U module from its rack or sub-rack slot, leaving the S5 front connector wired to the field untouched.
2. Install the S7-300 module (e.g., 6ES7 321-1BL00-0AA0 32DI) on the DIN rail.
3. Mount the matching S5-to-S7 adapter sub-rack adjacent to the S7-300 module.
4. Plug the existing S5 front connector onto the adapter sub-rack.
5. Use the short S7-300 front connector (supplied with the adapter) to bridge from the adapter to the S7-300 module header.
6. Address the S7-300 module in STEP 7 hardware configuration so that the S5 byte addresses used in the original S5 program map onto the corresponding S7 input/output bytes.

STEP 7 Conversion Tool and Program Migration

Program conversion is covered in detail by the STEP 7 — From S5 to S7 (S5S7_e.pdf) manual. The tool is integrated into the STEP 7 V5.x classic programming environment and operates on S5 STL source files exported from an S5 PG (or from the original S5 program printout). The tool output is an S7 STL source file that can be loaded into a STEP 7 S7 program and compiled.

Conversion flow

1. Generate an S5 STL source file from the S5 program: in PG 685/710/730/750, select File → Documentation → STL, or use the S5-DOS file transfer to extract the program from the memory submodule.
2. Open the S5 STL source in the S5 to S7 conversion tool inside STEP 7 V5.x (File → Convert S5 Files).
3. Assign a target S7 CPU and target program structure (S7-300 vs S7-400, single-project vs library integration).
4. Run the conversion. The tool emits an S7 STL file plus a conversion log.
5. Compile the S7 STL in STEP 7, address all warnings, and resolve any red (error) entries in the log.
6. Download the S7 program to the target S7 CPU and run the IO check.

What the tool handles automatically

• Direct S5 STL operations that map 1:1 to S7 STL operations (load, transfer, AND, OR, comparison, jump, timer, counter, integer math).
• S5 bit, byte, word, and double-word addressing mapped to S7 bit, byte, word, and double-word addressing.
• Standard S5 program blocks (OB, PB, SB, FB, DB) mapped to the equivalent S7 program block types (OB, FB, FC, DB, UDT). See the next section for the block-by-block mapping table.
• Standard S5 timer (T 0 to T 31) and counter (C 0 to C 31) word addresses mapped to S7 timer (T 0 to T 511) and counter (C 0 to C 511) word addresses.

What the tool does NOT handle automatically

• Vendor or user-written S5 function blocks that use absolute addresses outside the standard I/Q/F range. These blocks need manual re-coding.
• S5 special function blocks for IM, COM, and CP that have no direct S7 equivalent. They are replaced by S7 FB/FC calls into the S7 standard library.
• S5 COM packages (e.g., COM 115, COM 130, COM 525) for point-to-point, AS-511, and PROFIBUS. These have to be replaced with S7 CP modules (CP 340, CP 341, CP 440, CP 441) and the S7 standard library for point-to-point or PROFIBUS.
• S5 integrated custom machine code (CM code in FB 200/250 type blocks) that some third-party vendors used to embed assembly. These have to be re-written in S7 STL or SCL.

S5 to S7 Program Block and Address Mapping

The default mapping used by the S5 to S7 conversion tool is documented in the STEP 7 — From S5 to S7 manual. The key block-type mapping is summarized below.

The default address mapping is summarized below. The mapping is configurable in the conversion tool's Address assignment dialog.

Communication Migration: S5 COM Packages and PROFIBUS / Industrial Ethernet

The S5 family handled serial and fieldbus communication through dedicated COM packages loaded into the S5 CPU or into a separate CP (communications processor):

• COM 115 / COM 130 — point-to-point ASCII/3964R/RK512 over RS 232 / RS 422 / RS 485 on a CP 521, CP 523, CP 524, or CP 525.
• COM 525 — S5-as-slave PROFIBUS on CP 5431.
• COM 526 — point-to-point on CP 5440.
• COM 5430 / COM 5431 — S5 PROFIBUS master on CP 5430 / CP 5431.
• AS-511 driver — the PG-to-S5 programming port protocol.

None of these COM packages run on an S7 CPU. The S5-to-S7 migration substitutes:

• Point-to-point ASCII / 3964R / RK512 on an S5 CP 521 / CP 523 / CP 525 → S7 CP 340 / CP 341 / CP 440 / CP 441 with the S7 PtP library (FB 7 to FB 12 family in the S7 standard library).
• S5 PROFIBUS master on CP 5430 / CP 5431 → S7-300 CPU 31x with integrated PROFIBUS-DP interface (e.g., 6ES7 315-2EH14) plus the S7 PROFIBUS DP library.
• S5 PROFIBUS slave on CP 5431 (COM 525) → S7-300 / S7-400 with PROFIBUS-DP slave interface and the S7 PROFIBUS DP-Slave library (FB 192, FB 193, FB 194 family).
• Industrial Ethernet (S5 CP 1430 / CP 1440 with COM 143 / COM 144) → S7 CP 343-1 / CP 443-1 with the S7 Open Communication library or S7 connections configured in NetPro.

The S5 COM packages themselves are not portable. The COM 115/130/525/5430/5431 call interface in the S5 STL program is replaced manually by the S7 FB/FC calls. The S7 program keeps the same data block layout for the COM handshake area, so the rest of the application code does not need to change.

Spare Parts Strategy and Lifecycle Planning

Spare-parts availability is the single most common driver of an S5 to S7 migration. The Siemens S5 product family entered product phase 3 — spare-parts on demand years ago; the S5-115U and S5-135U/155U have now been in product phase 4 — phase-out for an extended period. Specific families to flag during planning:

For the S5-155H redundant CPU, the migration target is the S7-400H redundant system with the appropriate redundancy software package. The S5-CPU 948R (redundant firmware) is replaced by the S7-400H pair; the program conversion uses the same S5 to S7 conversion tool with the S7-400H as the target CPU. The Siemens S5 to S7 renewal manual has a dedicated section on S5-155H to S7-400H conversion that lists the analog and digital I/O module swaps and the redundant PROFIBUS-DP ring reconfiguration steps.

Step-by-Step Migration Procedure

The following procedure consolidates the conversion steps from the STEP 7 — From S5 to S7 manual and the SIMATIC S5 to S7 Migration Manual into a single, sequential runbook.

Prerequisites

• STEP 7 V5.5 SP4 (or later V5.x) installed on the engineering PG.
• S5 STL source of the program (printed or electronic). The S5 PG should be configured with the S5-DOS file transfer utility to dump the program files to a PC.
• STEP 7 license for the S5 to S7 conversion tool (option package in STEP 7 V5.x).
• Siemens S5-to-S7 adapter catalog (S5 S7_Adapter_Eng_V3_0.PDF) and the selected adapter family for every S5 I/O module on the bill of materials.
• S7-300 or S7-400 hardware (CPU, IM, SM, PS) configured to match the S5 rack I/O count.

Procedure

1. Export the S5 program. On the S5 PG, select File → Manage → Transfer → PC to dump all program blocks (OB, PB, SB, FB, DB) as STL files. Include the symbol table and the assignment list.
2. Document the S5 I/O wiring. Use the S5 wiring diagram or the S5 module pin-out labels (printed on the front connector flap). Cross-reference each S5 I/O byte (IB 0, IB 1, ..., QB 0, QB 1, ...) to a field device tag.
3. Match S5 to S7 I/O modules. For each S5 module (e.g., 6ES5 430-4UA14 digital input), identify the equivalent S7 module (e.g., 6ES7 321-1BL00-0AA0 32DI 24 V DC) and the matching S5-to-S7 adapter (catalog number from the S5 S7_Adapter catalog).
4. Run the S5 to S7 conversion tool. Open the S5 STL files in STEP 7 V5.x via File → S5 Files → Convert. Select the target CPU (e.g., 6ES7 315-2EH14-0AB0) and the default address mapping.
5. Resolve the conversion log. Every error in the log corresponds to a line in the converted S7 STL that needs manual correction (S5 special function call, vendor block, COM call, etc.). Resolve all errors and as many warnings as practical before proceeding.
6. Wire the S7 hardware. Mount the S7-300 / S7-400 modules on the DIN rail. Install the S5-to-S7 adapter sub-racks (S7-300) or adapters (S7-400) adjacent to the modules. Plug the existing S5 front connectors onto the adapters.
7. Download the converted S7 program. Connect the engineering PG to the S7 CPU (MPI / PROFIBUS / PROFINET, depending on the CPU variant). Download the hardware configuration, the S7 program, and the S7 symbol table.
8. Run the IO check. Force every S7 input and observe the corresponding input LED. Force every S7 output and observe the actuator. Document the result for every channel on the S7 IO list.
9. Run the converted program in OB 1. Put the S7 CPU in RUN with the converted program loaded. Monitor with STEP 7 Monitor / Modify in the test mode. The HMI / SCADA tag list should resolve directly to the S7 symbols that the conversion tool re-used from the S5 symbol table.
10. Sign off and back up. Dump the S7 program and the S7 symbol table to the project's version-control system. Store the S5 to S7 conversion log with the project for future audits.

Verification, IO Checkout, and Troubleshooting

After the converted S7 program is downloaded and the IO is wired through the adapters, the verification phase has four parts: power-up, IO check, functional test, and sign-off.

Power-up verification

1. Verify the S7 PS (power supply, e.g., 6ES7 307-1EA01-0AA0 for S7-300) is wired to the 24 V DC input and that the output voltage is within ±5 % of the rated value (24 V DC ±5 %).
2. Verify the S7 CPU is in STOP and the SF (system fault) and BF (bus fault) LEDs are off. A steady SF LED with no program loaded is normal on some S7-300 CPUs.
3. Verify the wiring adapter stack: S5 front connector → adapter → S7-300 / S7-400 module. Confirm the front connector latch is fully engaged and the locking screw is tightened.

IO check

1. In STEP 7, open the S7 program and connect to the S7 CPU online.
2. Use Monitor / Modify to read each input byte (e.g., IB 0). For digital inputs, force the field sensor on and verify the corresponding bit toggles. For analog inputs, read IW 0 (or IW x) and verify the scaled value matches the field transmitter (e.g., 4 mA → 0, 20 mA → 27648 raw).
3. Use Modify in Modify Peripheral Outputs mode to write to each output byte. Confirm the actuator or the input LED of the next-stage device responds. For analog outputs, write 27648 (full scale) and verify the field signal is the rated current or voltage.

Functional test

1. Switch the S7 CPU to RUN with the converted program loaded.
2. Run the machine through every operating mode (manual, auto, jog, half-auto) and every recipe or setpoint. Compare the HMI trending with the S5 baseline if one is available.
3. If a HMI (ProTool / WinCC flexible / TIA Portal HMI) is bound to the S5 program via PROFIBUS or Ethernet, re-bind the HMI tags to the S7 symbols. The S5 symbol table is preserved by the conversion tool, so the HMI tag list import is direct.

Troubleshooting matrix

Field-Commissioning Notes

Three field-proven points are worth flagging before the cutover:

1. Front connector gender. S5-115U modules use screw-type front connectors with screw-clamp or cage-clamp terminations. S7-300 modules use screw-type or spring-type front connectors in a different mechanical form factor. The S5-to-S7 adapter bridges the two; it is not a gender-changer. Do not skip the adapter and try to wire the S5 field conductors directly onto the S7 module — the pitch and the labeling do not match.
2. Galvanic isolation. Some S5-115U analog modules had 12-bit resolution (e.g., 6ES5 460-4UA13) while the S7-300 SM 331 6ES7 331-7Kxxx is 13-bit resolution (default) or 16-bit (configured). The converted S7 program will read the new module at the new resolution; the scaled engineering value will change. Update the analog scaling in the S7 program or in the HMI to match the new resolution.
3. Memory submodule migration. The S5 EPROM/EEPROM submodule is not usable in an S7 CPU. The converted S7 program lives in the S7 MMC (Micro Memory Card) or in the S7 CPU's load memory. Always back up the S7 MMC at the end of commissioning and store a copy with the project documentation.

FAQ