Resolving TRCV_C Error 80C3 on S7-1500 Open User Communication

Problem Overview: TRCV_C #80C3 on S7-1500 Open User Communication

The TRCV_C and TSEND_C instructions implement open user communication (OUC) over the integrated PROFINET interface of the SIMATIC S7-1200 and S7-1500 CPU families. Both blocks combine three legacy functions: TSEND_C wraps TCON, TDISCON, and TSEND; TRCV_C wraps TCON, TDISCON, and TRCV. The combined design lets a single FB own the entire connection lifecycle while exposing a compact status interface (DONE, BUSY, ERROR, STATUS, NDR, RCVD_LEN).

When TRCV_C reports STATUS = 16#80C3, the embedded TCON sub-function has failed. The S7-1200/S7-1500 communication manual defines this status as "All connection resources are in use." In practice the failure mode splits into two distinct causes: a duplicate local CONN_OUC ID, or a fully populated connection resource table. The original report — a CPU 1515F2-PN driving 4 PCs each with 3 telegrams (12 simultaneous OUC connections) — is on the edge of the published resource budget for the F-class 1500, and the path to #80C3 is dominated by resource accounting, not by network quality. See the official block description at TSEND_C and TRCV_C — Send and receive data using Ethernet.

Where #80C3 Originates in the Block

Inside the combined FB, the TCON sub-function performs the connection resource allocation. TCON is invoked on the rising edge of CONT or when the instance DB has just been (re)initialized. If the CPU's kernel-side connection table already holds an entry for the requested ConnId, or if the table is full for the protocol/interface pair requested (TCP, ISO-on-TCP, UDP, or others), TCON returns 0x80C3 to the user block. TRCV_C mirrors that status on the STATUS output and the ERROR/STATUS pair at the rising edge of NDR.

The TIA Portal "Connections" editor view is a logical, configuration-time representation of the connection topology. It does not reflect the kernel's runtime state. A mismatch is normal during a startup race and during TIA Portal download sequences. Always trust the block's online STATUS over the editor's view.

Full error tables are published in the S7-1200 communication manual: Legacy TSEND_C and TRCV_C — Send and receive data using Ethernet.

CPU 1515F2-PN Connection Resource Accounting

The 1515F2-PN shares a fixed pool of connection resources among PROFINET IO, S7 communication, OUC, Web server, OPC UA server, HMI panels, and the engineering/TIA Portal online channel. The F-class variant additionally reserves slots for PROFIsafe. The exact published maximum depends on the firmware version and is documented in the device manual. With 4 partner PCs and 3 telegrams per PC you are asking the kernel to manage 12 active OUC connections from a single program — every connection needs a unique ConnId in the local connection table, and a matching unique identifier at the partner.

Symptom Matrix

Diagnostic Procedure

1. Open TIA Portal and navigate to Devices & Networks → Connections. List every TSEND_C/TRCV_C block and its configured ConnId (also called CONN_OUC ID). Highlight any duplicate IDs.
2. Open each TRCV_C instance DB (for example DB2100) in online mode. Confirm the STARTUP bit in the STATIC section is FALSE after a download. A TRUE value indicates the DB was reinitialized.
3. Create a watch table that includes the STATUS and ERROR outputs of every block. Force the CPU to RUN. Watch for the first instance that reports ERROR=TRUE STATUS=16#80C3.
4. From the same watch table, monitor the CPU's online connection list via Online & Diagnostics → PROFINET interface → Connection list. Cross-reference every connection shown against the configured ConnId values.
5. If the online connection list shows fewer entries than configured IDs, the missing entries are the ones that failed TCON — those are the blocks that reported #80C3.
6. From the project tree, right-click the CPU → Online & Diagnostics → Diagnostic buffer. Look for the Communication error events. The Mode field shows the event class; the Event ID for OUC resource exhaustion is the same as the STATUS code returned by the block.

Connection Topology Reference

Solution 1 — Eliminate Duplicate CONN_OUC IDs

The TCON_Parms structure inside the TSEND_C/TRCV_C data block contains a ConnId field. In TIA Portal this is exposed as the Connection ID (also called CONN_OUC ID) property on the block's configuration dialog. Every active OUC connection — TSEND_C, TRCV_C, TCON, or the legacy TCP/ISO-on-TCP variants — must use a unique ConnId. The ID space is local to the CPU; PCs at the other end of the cable do not need to match.

For a 1515F2-PN with 12 OUC connections, the recommended practice is to allocate a 16-wide block per protocol direction. The ConnId values 1..15 are reserved by TIA Portal for system connections; start at 100 to leave a generous gap.

Reserve ConnId 124..127 as sentinels. If a code review spots one of those IDs in a user program, an earlier developer misallocated the ID space.

Solution 2 — CONT Reset Pattern (Field-Proven)

When the kernel refuses to release a connection slot and the only documented recovery is a power cycle, a forced CONT = FALSE → CONT = TRUE toggle at the block input forces TDISCON followed by TCON. The pattern below runs in OB1 and self-heals any TRCV_C/TSEND_C that reports ERROR with a recoverable status (including 0x80C3).

// ST / SCL — TRCV_C self-healing wrapper
// iDB_TRCV is the instance DB of TRCV_C (e.g. DB2100)
// tReset is a TON timer instance
// bResetLatch is a static BOOL

IF iDB_TRCV.ERROR
   AND (iDB_TRCV.STATUS = 16#80C3
        OR iDB_TRCV.STATUS = 16#80C4
        OR iDB_TRCV.STATUS = 16#80C7) THEN
    tReset(IN := TRUE, PT := T#200ms);
END_IF;

IF tReset.Q THEN
    iDB_TRCV.CONT := FALSE;     // forces TDISCON
    bResetLatch   := TRUE;
END_IF;

iDB_TRCV();                     // call block

IF bResetLatch AND NOT iDB_TRCV.BUSY THEN
    iDB_TRCV.CONT := TRUE;      // re-arm TCON on next cycle
    bResetLatch   := FALSE;
    tReset(IN := FALSE);
END_IF;

The same pattern scales to a function block that wraps a single TRCV_C plus the reset logic, instantiated 12 times. Variants observed in production code include a watchdog timer that cycles CONT low for 200 ms then high, and an HMI tag that drives CONT to allow operator-initiated reset without a STOP/RUN download.

Solution 3 — Instance DB Reinitialization on Download

Every TIA Portal download can reinitialize the TRCV_C/TSEND_C instance DB if the block's interface signature has changed (added STATIC, changed TEMP, recompiled). When the DB is reinitialized, the internal "connection already established" flag is cleared, the block issues a new TCON, and that new TCON collides with the still-open kernel connection — resulting in #80C3 for one scan. The TIA "Connections" view will momentarily show 13 entries until the old one times out.

To prevent the post-download collision:

1. Open the instance DB properties → Download tab. Uncheck Reinitialize instance DB on download if the project policy allows it.
2. Wrap every TRCV_C/TSEND_C call with the CONT reset pattern (Solution 2). A reinitialized DB has CONT=FALSE on its first scan, so the block will re-TCON cleanly.
3. For the first download after a program change, perform a STOP → MRES → RUN on the CPU to flush the kernel's connection table before the user program starts. MRES resets the connection table; a warm restart (STOP → RUN) does not.

Firmware Considerations

The original report references firmware V2.0 on the CPU 1515F2-PN. V2.0 is early for the F-generation 1500; later firmware versions (V2.6, V2.9, and the V3.x line introduced with TIA Portal V18/V19) fix several open-user-communication defects observed in earlier branches:

• Improved handling of the CONT edge after a TCON failure — blocks no longer leave a partially-allocated resource slot in the table.
• Additional resource headroom for OUC on PROFINET interface X1 and X2 (where present on the CPU variant).
• Fixes for a TRCV_C leak in which a #80C3 on the first call would not release the resource until the next STOP/RUN.
• Hardened handling of ISO-on-TCP partner TCON collisions during partner restart storms.

Before applying any firmware update, capture the current project, perform a full backup using the SIMATIC Automation Tool, and review the release notes for breaking changes in TCON_Parms structure layout. TIA Portal must be the matching version: V2.6 → TIA V15.1, V2.9 → TIA V16 Update 4 or later, V3.0 → TIA V17, V3.1 → TIA V18/V19. The full compatibility matrix is in the Siemens online support entry 67196808 — How do you program the TSEND_C and TRCV_C instructions for open user communication over the integrated PROFINET interface of the S7-1200/S7-1500 CPU?

Worked Example: 1515F2-PN with 4 PCs × 3 Telegrams

Assume the application needs three unidirectional data exchanges per PC:

• Telegram 1: PLC → PC, 256 bytes, every 100 ms (control setpoints).
• Telegram 2: PC → PLC, 512 bytes, event-driven (acknowledgements).
• Telegram 3: bidirectional, 1024 bytes, every 1 s (diagnostic block).

TRCV_C supports a maximum payload of 8192 bytes per the S7-1200 manual. All three telegrams fit comfortably. The total OUC connection count is 4 PCs × 3 = 12, each occupying one slot in the kernel's connection table. Add PROFINET IO, the HMI connection, and the engineering connection, and the CPU is operating near its published resource limit. If the limit is exceeded, the kernel refuses TCON with #80C3 even though the project compiles cleanly.

Two engineering choices reduce the load: (a) collapse two unidirectional telegrams into a single bidirectional exchange (1 connection instead of 2), or (b) move lower-priority exchanges to a single multiplexed connection with a length-prefixed protocol. Either approach halves the OUC count and provides headroom for future expansion.

Verification Procedure

1. Download the corrected program. Force the CPU to STOP, then RUN.
2. Open a watch table with STATUS of all 12 blocks. All must show 16#0000 (no error pending) within 5 s of RUN.
3. From TIA Portal Online & Diagnostics, navigate to PROFINET interface → Connections. Confirm exactly 12 OUC entries plus the engineering connection.
4. Disconnect one PC's Ethernet cable. The corresponding TRCV_C should report 16#80C7 (timeout) and TSEND_C should report 16#80C4 (connection terminated). All other 11 connections must remain unaffected.
5. Reconnect the cable. The CONT reset pattern (Solution 2) must restore the connection without a STOP/RUN of the CPU.
6. Trigger a TIA Portal download of a non-communication-related block. All 12 connections must survive the download (the instance DBs are not reinitialized, the kernel does not release the resources).
7. Read the diagnostic buffer. No Communication error events with ID 0x80C3 should appear during the test sequence.

Troubleshooting Matrix

Preventive Best Practices

• Maintain a centralized ConnId allocation table in the project documentation. Review it at every code review.
• Always wrap TSEND_C/TRCV_C in a self-healing FB that toggles CONT on #80C3 or #80C7.
• Enable the Block consistency check during TIA Portal download so that unintended reinitialization of instance DBs is reported.
• Use distinct PROFINET interface X1/X2 (if available on the CPU) to spread OUC and PROFINET IO across separate MAC tables.
• Schedule firmware updates through the Siemens release cycle. Subscribe to the firmware RSS feed for the 1515F2-PN to be notified of OUC bug fixes.
• Avoid TCON/TDISCON raw blocks in the same program as TSEND_C/TRCV_C. Mixing the two families on the same ConnId is a known recipe for resource table corruption.
• Document the maximum expected OUC count per CPU in the network architecture diagram. Add a 20% headroom margin; never operate at the published maximum.

FAQ