SIMIT / PLCSIM Advanced Timing and Synchronization Modes

Supplementary detail on how time is actually kept in sync across an MCD + SIMIT + PLCSIM Advanced virtual commissioning stack — a topic official docs describe procedurally but that practitioner/industry writeups explain more in terms of why it matters and what can go wrong.

Two fundamentally different timing modes

Industry coverage of Tecnomatix/PLCSIM Advanced virtual commissioning (applicable to the same underlying PLCSIM Advanced engine used in MCD workflows) describes two timing regimes:

• Real-time mode with time scaling: time progression between S7-PLCSIM Advanced and the connected simulator (Process Simulate, or by extension NX MCD/SIMIT) is synchronized, with support for time-scaling factors between 0.01x and 100x real-time speed. This is useful for either slowing down fast mechanisms for detailed observation (0.01x) or accelerating long-duration sequences for faster iteration (up to 100x).
• Synchronization-point (lockstep) mode: the simulation runs to a defined sync point and then pauses until the external simulator explicitly signals "continue." This is described as the correct mode "for a digital twin or hardware-in-the-loop style environment" — i.e., when you need deterministic, exact correspondence between simulated PLC scan cycles and simulated physics steps rather than best-effort real-time approximation.

Source: https://www.automationworld.com/products/control/blog/13320025/virtual-commissioning-of-a-robotic-cell

Multi-PLC coordination requires explicit pacing

Research on multi-PLC virtual commissioning scenarios found that when coordinating multiple PLCs within a single PLCSIM Advanced environment, maintaining synchronization required explicitly enabling simulation pacing and setting the pacing factor to 1. Without this, independent PLC instances can drift out of sync with each other and with the physics simulation, defeating the purpose of a synchronized virtual commissioning setup. This is a specific, actionable configuration detail for anyone extending a single-PLC MCD virtual commissioning setup to a multi-controller line.

Source: aggregated from search-indexed academic/technical coverage of PLCSIM Advanced multi-PLC scenarios (query results referencing ResearchGate publications on Tecnomatix Process Simulate + PLCSIM Advanced integration).

Practical takeaway for MCD-specific workflows

Although the sources above are drawn from the closely related Tecnomatix Process Simulate ecosystem rather than NX MCD directly, they use the same underlying S7-PLCSIM Advanced engine and the same two timing paradigms (real-time+scaling vs. sync-point lockstep) that NX MCD's own virtual commissioning connections rely on. If an MCD-based virtual commissioning session shows drift, jitter, or inconsistent behavior between runs, check which of these two modes is active and whether pacing is configured appropriately for the number of controllers involved — this is a more precise diagnostic starting point than generic "check your network" troubleshooting advice.