Resolving TSEND Error 80A1 on S7-300 315F-2 PN/DP with Zebra

Problem Overview

When a Siemens SIMATIC S7-300 CPU 315F-2 PN/DP (firmware V3.2.x) attempts to send print jobs to a Zebra ZM400 industrial label printer over the integrated PROFINET interface using the standard open-TCP communication blocks (FB63 TSEND, FB64 TRECV, FB65 TCON, FB66 TDISCON), the user program repeatedly receives status code 80A1 on the TSEND block. The same status also appears on the TCON status output if connection setup is monitored. Even though the CPU can ping the printer on IP 10.8.100.101 and both devices sit in the same subnet, the TCP socket at the application layer never becomes fully established and no label data is delivered.

Status 80A1 in the Siemens TSEND / TCON family does not mean the cable is bad or the IP stack is broken. It means: "The connection is not yet established – a TSEND/TRECV was issued before TCON reported DONE, or the existing connection was torn down by the partner, by the CPU, or by a restart." The reference numbering of the open TCP/ISO-on-TCP blocks on S7-300/400 is FB63/64/65/66 (TSEND_C, TRCV_C, TSEND, TRCV, TCON, TDISCON). On S7-300 firmware V3.x the legacy numbering is preserved. For the official Siemens description of the error semantics, see the SIMATIC NET FB63–FB66 block manual and the TCON / TSEND / TRECV programming guideline.

Affected Hardware and Firmware

Root Cause Analysis

Error 80A1 on a 315F-2 PN/DP is almost always one of three layered causes. They can occur in isolation or in combination.

1. Connection establishment is not requested in OB100. The integrated PROFINET stack of the 315F-2 PN/DP releases the open-TCP connection table only after OB100 has run once. If the user program only calls TCON in OB1 and the CPU is in RUN before the connection is up, the first TSEND call in OB1 issues against a not-yet-existing connection and returns 80A1. A subsequent Stop→Run (warm restart) does not always rebuild the table – a true cold restart is required.
2. Local port number is outside the firmware-permitted range or is duplicated. Older firmware revisions of the 315F-2 PN/DP only allow local ports 2000 to 5000 for open-TCP. Even within that range, if a port is reused for two active connections with different IDs, the second TCON will fail with 80A1 because the kernel refuses the second bind. The user program reports 80A1 on the next TSEND against the failed connection.
3. The TCON parameter block (UDT 65 "TCON_PAR") is incomplete or mismatched. The most common field mistakes are: InterfaceID pointing to the wrong HW identifier (must be the PROFINET interface, not the PROFIBUS side), ActiveEstablished = TRUE for a connection that should be passive, or ConnectionType = 18 (ISO-on-TCP) where the Zebra printer only speaks raw TCP – the partner then resets the socket and the next TSEND returns 80A1.

Connection ID and Local Port Rules

Open-TCP on the 315F-2 PN/DP enforces a flat connection table. Every connection — active or passive — must have a unique connection ID in the range 1 … 4095 (in practice the FB65 input ID). Each unique ID also implies a unique local port if the CPU is the active side. A typical mistake is to reuse ID := 5 across two S7 connections that happen to terminate at the same Zebra – the second TCON replaces the first and the printer sees the second socket as the only valid one, while the first connection state machine in the CPU continues to issue TSEND against a now-orphaned ID, producing 80A1.

UDT 65 (TCON_PAR) Field Reference

The TCON block expects its CONNECT input to point at a data block of type UDT 65 "TCON_PAR". The fields most often wrong on a 315F-2 PN/DP open-TCP project are listed below. Values shown are the values that resolve the 80A1 symptom for a CPU → Zebra ZM400 raw-socket link.

LocalAddress byte layout for the CPU side (port 2500 = 0x09C4):

LocalAddress[1] = B#16#0A   // 10
LocalAddress[2] = B#16#08   // 8
LocalAddress[3] = B#16#64   // 100
LocalAddress[4] = B#16#01   // 1  (CPU's own IP — fill with whatever the CPU actually has)
LocalAddress[5] = B#16#09   // 2500 high
LocalAddress[6] = B#16#C4   // 2500 low

Step-by-Step Solution

The fix is the same regardless of whether you build the user program in STEP 7 V5.5 with the legacy F-library or in TIA Portal V13+ with the Open Communication instructions. The sequence is: (1) configure HW, (2) drop the right FB in OB100, (3) drop the cyclic FBs in OB1, (4) cold-restart, (5) watch DONE.

Step 1 — Hardware and network configuration

1. In HW Config / device view, open the PROFINET interface properties of the CPU. Confirm IP address (e.g. 10.8.100.1) and Subnet mask 255.255.255.0. The Zebra ZM400 must be in the same subnet (10.8.100.101 / 24).
2. Open Options > Configure Network (NetPro) and select the PROFINET subnet. Do not enable routing for an open-TCP link – routing is a Layer-3 service and is not needed for a same-subnet CPU↔printer socket. (Routing can coexist, but on V3.2 it occasionally causes TCON timeouts that surface as 80A1.)
3. Verify with ping 10.8.100.101 from a programming PC and a separate PG/OP connection ping from the CPU's online diagnostics. Both directions must succeed. Unidirectional ping = duplex mismatch, almost always a bad patch cable or a forced-100 Mb/s negotiation on one side.

Step 2 — Place the connection-establishment logic in OB100

This is the operationally critical step. Create or open OB100 (Complete Restart / Cold Restart) in your S7 program. Place a single call of FB65 TCON there with the UDT 65 parameter block described above. Example call (STEP 7 classic STL notation shown for clarity; TIA Portal uses the same inputs through the instruction box):

// OB100 — complete restart
CALL  FB65  "TCON"          // Open TCP connection
  REQ    :=TRUE             // Fire on every cold restart
  ID     :=W#16#5           // Connection ID 5, must be unique
  DONE   :=M100.0           // Becomes TRUE once the socket is up
  BUSY   :=M100.1
  ERROR  :=M100.2
  STATUS :=MW102            // 80A1 / 80A7 / 0000 etc.
  CONNECT:="TCON_PAR_ZM400".TCON_PAR  // UDT 65 in instance DB

Step 3 — Place cyclic TCON / TSEND / TRECV in OB1

OB1 is the cyclic supervisor. It must re-issue TCON while DONE = FALSE and only start firing TSEND once DONE = TRUE. Recommended logic:

// OB1 cyclic
// 1. Hold TCON active until DONE
A   M100.0            // DONE
JC  SEND              // If socket up, skip TCON call
CALL FB65 "TCON"
  REQ    :=TRUE
  ID     :=W#16#5
  DONE   :=M100.0
  BUSY   :=M100.1
  ERROR  :=M100.2
  STATUS :=MW102
  CONNECT:="TCON_PAR_ZM400".TCON_PAR

SEND: NOP 0
// 2. Only call TSEND when DONE = TRUE and the print buffer is non-empty
A   M100.0            // DONE
A   "PRINT_REQ"       // Trigger from HMI / recipe
JC  DO_SEND
JU  RCV

DO_SEND: CALL FB63 "TSEND"
  REQ    :="PRINT_REQ"
  ID     :=W#16#5
  LEN    :="PRINT_LEN"   // Byte length of the ZPL command string
  DATA   :=P#DB100.DBX0.0 BYTE 200   // ZPL II command buffer
  DONE   :=M104.0
  BUSY   :=M104.1
  ERROR  :=M104.2
  STATUS :=MW106

RCV: CALL FB64 "TRECV"
  ID     :=W#16#5
  LEN    :=200
  DATA   :=P#DB101.DBX0.0 BYTE 200
  NDR    :=M108.0
  ERROR  :=M108.2
  STATUS :=MW110
  LEN_R  :=MW112

Step 4 — Cold-restart the CPU

1. From STEP 7 / TIA Portal: Online > CPU Operating Mode > Cold Restart. Confirm the CPU prompt. The CPU goes to STOP, executes OB100 (where the TCON is fired), then transitions to RUN.
2. Watch STATUS in VAT. After 1–3 OB1 cycles the value must change from 80A1 to 0000 and the DONE bit must rise. 80A7 during the transition means the Zebra closed the socket – check cabling and printer IP.
3. Force a one-shot ZPL command through, e.g. ^XA^FO50,50^A0N,50,50^FDHello^FS^XZ. Verify the label prints.

Step 5 — Persist the connection across power-cycle

Place the same OB100 TCON call in OB101 (Restart / Warm restart) as well. On 315F-2 PN/DP firmware V3.2, the open-TCP table is not rebuilt automatically across a warm restart. OB101 ensures the connection is re-issued if the operator only triggers a restart and not a full cold restart.

Verification Procedure

Extended Troubleshooting Matrix

Zebra ZM400 Specific Notes

• Port 9100 is the ZPL raw socket. ZM400 firmware revisions older than V53.16.5Z do not close the socket when a print job finishes, which is the desired behaviour for an S7 print trigger – the CPU keeps one long-lived socket and writes multiple ZPL commands into it.
• The Zebra replies with short status strings on the same socket (e.g. ERROR 1234). Use the FB64 TRECV call in OB1 to drain these into a receive DB and parse them in the user program. A TRECV error 80A7 with a healthy TSEND means the printer reset the socket – almost always a malformed ZPL string.
• If multiple printers are on the line, assign each a unique remote port (9100, 9101, 9102 …) and a unique connection ID. The 315F-2 PN/DP supports up to 8 active TCP connections on firmware V3.2.

Safety (F-CPU) Considerations

The CPU 315F-2 PN/DP is fail-safe. Open TCP communication via FB63–FB66 is a standard user-program function and is not safety-related. The F-runtime will not interfere with it as long as the F-shutdown is not asserted. If the F-CPU goes to F-STOP, OB1 stops executing and TSEND will not be called. This is the correct behaviour – a printer must never be the arbiter of a safety function. The 80A1 that appears in F-STOP is expected and does not need to be cleared; clear it by leaving F-STOP.

Commissioning Checklist

• CPU firmware V3.2.x confirmed (online → Module Information → Firmware).
• PROFINET X2 IP and subnet correct, gateway left blank for direct link.
• Routing disabled for the open-TCP subnet, or verified non-conflicting.
• FB65 TCON called in OB100 and OB101.
• UDT 65 fields: ConnectionType = 17, LocalDeviceId = 2, ActiveEstablished = TRUE, RemoteAddress[5..6] = 0x23, 0x88 (port 9100).
• Local port 2500 (or any port in 2000–5000 not used by S7 / HTTP / PROFINET services).
• Cold restart performed after program download.
• TCON STATUS = 0000, DONE = TRUE within 2 s of RUN.
• Test ZPL string prints, Zebra log shows the job.
• TRECV in OB1 drains printer status replies into a receive DB.