Simulate a Missing S7 Partner for a PCS 7 Virtual Controller in SIMIT

Choose between testing the S7 communication and substituting received data for AS logic tests. SIMIT V10.2 supports specified S7 communication blocks, so the presence of connections to an unavailable partner is not itself a universal simulation prohibition. However, reproducing an unknown black-box controller requires its interface behavior. When that information is unavailable, documented DB-write components offer a narrower way to exercise known receiving logic, with explicit limits: they do not validate the network connection or the real partner application.

Separate Network Testing from Logic Testing

A PCS 7 project imported into a SIMIT Virtual Controller can contain S7 connections to a separate machine controller whose project is unavailable. The first decision is whether the test must validate the actual S7 exchange or only the AS logic that consumes received data.

SIMIT V10.2 documents supported S7 communication between Virtual Controllers and between a Virtual Controller and an external device. Its supported-block tables include BSEND/BRCV, GET/PUT and USEND/URCV. A blanket assertion that such connections cannot be simulated is therefore incorrect. This does not establish a generic chart component that reproduces an unknown machine controller's application protocol. SIMIT manual, chapters 3.6.1.6–3.6.1.7

Option 1 — Provide a Defined Communication Partner

Use this approach when connection establishment, application handshakes and communication failures are part of the acceptance criteria.

Before implementation, identify the actual send/receive blocks, connection configuration, data layout, data ownership and application-level sequence from the available AS project and authorized interface documentation. These are project-specific requirements, not values that can be inferred from the fact that the partner uses Siemens hardware.

A separate simulated or physical test partner must implement that documented interface and use a communication path supported by the installed SIMIT release. Without the partner application or an adequate interface specification, its responses and failure behavior cannot be reproduced faithfully. A newly engineered stand-in is an adaptation requiring validation, not a verified replacement for the unavailable machine project.

Option 2 — Substitute Defined DB Values for Logic Tests

Use data substitution when the purpose is to exercise downstream AS logic and the received-data locations are known. This bypasses the network exchange; it cannot prove S7 connection operation.

For SIMIT V10.2, the manufacturer documents controller DB access through basic-library components. A documented implementation uses WriteDatablock:

Work in an isolated simulation project and save the Virtual Controller coupling.
Add WriteDatablock from COMMUNICATION | SIMATIC.
Configure a unit connector with the coupling name and connect it to the component's Gateway input.
Set DB to the intended data-block number and DBB to its first byte address. Obtain both from the actual project.
Supply the intended bytes at X1 through XN. The documented component supports up to 32 bytes per operation.
Trigger a write with a rising edge at Trigger, and inspect the receiving AS logic.

The manual specifies one initialization write even before a trigger is sent. Account for it in the test setup. Byte encoding, ownership and handshake timing remain project-specific engineering work. SIMIT manual, pp. 211 and 586

Verification

For a network test, observe the actual communication-block results and the defined application handshake at both ends. Confirm that the chosen test partner supplies the correct data under the planned scenarios; a Virtual Controller in RUN is insufficient proof.

For substitution, inspect the targeted DB before and after a controlled write and verify the resulting downstream logic. Check that the simulated controller program does not immediately overwrite the injected data or depend on a communication-status signal that substitution does not reproduce.

Keep network-test results separate from logic-substitution results. The latter can support downstream functional testing while leaving connection behavior unverified.

Limitations and Operational Precautions

The verified component names and behavior are from SIMIT V10.2; the affected installation's exact release was not specified. The available information does not establish the black-box controller's message layout, response logic or a complete replacement model.

Do not connect a test partner or write component to a production controller unintentionally. Preserve the simulation project and identify writable DB ranges before testing. Do not inject arbitrary values into safety-related or command data, and do not describe substituted data as evidence that network diagnostics, timeouts or the real partner application have been validated.

Engineer FAQ

Must the black-box controller's project be imported to test any AS logic?
No. Defined DB-value substitution can exercise selected receiving logic, but cannot reproduce unknown partner behavior or validate its S7 connection.

Is a SIMIT chart automatically an S7 protocol emulator?
No such general behavior is established. The documented DB-write component changes controller memory rather than implementing the remote application protocol.

Technical References

Siemens — SIMIT Simulation Platform V10.2 Operating Manual, March 2020, A5E44876249-AB — chapters 3.6.1.6–3.6.1.7 supported communication; chapter 3.13.1.7, p. 211, coupling access; basic-library WriteDatablock, p. 586.

SIMIT S7 communication simulation

Simulate a Missing S7 Partner for a PCS 7 Virtual Controller in SIMIT