Configure PCS 7 APL Communication Blocks Before Their First Call

You do not necessarily need to schedule a cold restart merely because APL communication blocks are newly added. The key is whether their connection parameters are configured before the block instance first initializes: the source's APL manual excerpt says ID is applied on the first call after a cold restart and R_ID on the first call after a warm restart, while the reply clarifies “first call” does not mean a restart must immediately precede it. Confirm the exact APL release and block documentation before changing a live communication instance.

What ID and R_ID identify

The APL communication-block manual describes ID as the connection number from the configured S7 connection and R_ID as an identifier that must match between corresponding send and receive blocks. These parameters bind the program blocks to the configured connection and partner; they are not interchangeable.

Set parameters before the initial block call

When adding a new communication-block instance, configure its NetPro connection and matching ID/R_ID values in the project before compiling and downloading the instance for its first execution. This avoids deliberately scheduling a cold restart solely to make the newly configured values available. The source reply specifically corrects the interpretation of “first call”: it need not be the first call after a recent CPU restart.

If the block already ran with unconfigured values

The ticket does not establish how to reinitialize an already executing instance whose connection parameters were first applied incorrectly. Do not assume that changing the constants online will rebind an existing instance safely. Follow the exact version's APL/BSEND-BRCV documentation and determine whether the configured block supports runtime parameter changes or requires instance reinitialization.

Commissioning procedure

Configure the S7 connection in NetPro for the applicable AS pair and record its connection ID.
Set the send and receive block parameters to matching, project-unique values as required by the exact APL communication-block manual.
Add the communication blocks and parameter values together before their first execution; compile and review the generated project configuration.
Download only through the approved PCS 7 change procedure and observe block status/diagnostics.
Verify the pair exchanges the intended data and reports healthy communication before relying on it operationally.

Do not cold-restart a running plant just to apply new values

A cold restart can disrupt process data and controller operation. The ticket says the plant does not allow one; this is a valid constraint, not a reason to bypass lifecycle safeguards. Design the change so the parameters are correct before first call or obtain version-specific guidance for safe reinitialization of an existing instance.

Verification

Check both sides' connection configuration, matching identifiers and block diagnostics. Confirm a deliberate value change at the sender is received at the intended partner with valid quality/status. A compiled project or successful download alone does not prove the connection is communicating correctly.

Limitations and Operational Precautions

The source omits the exact APL version and does not describe the state of the existing instances when parameters were changed. A later Industry Library manual documents runtime parameter reconfiguration in its S7RcvDig wrapper; that does not prove every APL block/version supports the same behavior. Confirm the actual block interface and lifecycle before editing live parameters.

Engineer FAQ

Does “first call” always mean first call after a restart? No. The source reply explicitly says it means the instance's initialization call, not necessarily a new restart event.

What does ID represent? The configured S7 connection number.

What must R_ID do? Match at corresponding send/receive partners and be unique for the connection pair as specified by the applicable manual.

Can an existing instance be changed online? Do not assume so; check the exact block/version's runtime parameter behavior.

Can I cold-restart to apply the change? Only under an approved process procedure; the source's plant does not permit it and does not need a restart merely to initialize a newly added, preconfigured block.

Technical References

Siemens, PCS 7 Advanced Process Library V9.0 SP2 Function Manual, section 20 “Communication blocks,” including Snd_DigVal: https://support.industry.siemens.com/cs/attachments/109760968/s7jal90b_en-US.pdf
Siemens, PCS 7 Industry Library for S7 V9.1 Function Manual, communication-block ID/R_ID parameter context and runtime reconfiguration: https://support.industry.siemens.com/cs/attachments/109805918/S7IL91b_en-US.pdf