SINUMERIK 840D V24 Transfer: Resolving Archive and Syntax Errors

Problem Overview

The SINUMERIK 840D operator panel front interface (V24 / RS-232-C) is commonly used to archive and restore part programs (.MPF / .SPF) and to push modified NC code from an external programming station into the controller. Two recurring fault conditions appear on the HMI when a transfer is attempted from a PC to the control but the file lands in the wrong format or the serial framing does not match:

1. "Die Datei ist kein Archiv" – the HMI parser rejects the incoming byte stream because the leading header bytes do not match the SINUMERIK archive signature. The control expects either a pure 7-bit ASCII Punch-Tape stream or a binary %_N_ archive container with block-check characters (BCC) and a closing %%EOF. Anything else is flagged as a foreign binary and rejected as a non-archive.
2. "Syntax error: please check file/pathname" – raised by the HMI loader when the framing (parity, stop bits, baud rate) drifts or when the line-discipline protocol (RTS/CTS vs Xon/Xoff) drops characters, producing truncated program headers that the parser cannot interpret.

The combination produces a one-way symptom: read from NC to PC works, but write from PC to NC fails. The asymmetry is the diagnostic fingerprint: outbound RS-232 framing is set on both ends correctly, but inbound framing on the HMI input screen, or the format selector, is misconfigured.

Root Cause Analysis

Three independent configuration layers must agree between the PC terminal program (e.g. SIMATIC ProTool/ProAgent terminal, Windows HyperTerminal, Tera Term, or the SINUMERIK-side equivalent "Services") and the HMI. Mismatch on any one layer produces the symptoms above.

Layer 1 – File Format (Punch Tape vs Archive)

The 840D HMI accepts two on-the-wire file representations on the V24 channel. According to the official Siemens documentation Setting V24 in the program manager (SINUMERIK 840D sl/840Di sl/828D):

• Punch Tape – plain ASCII, line-oriented, ISO 7-bit. Each NC block ends with LF. The file is the exact text that would appear in the editor. No BCC, no header, no trailer. This is the format produced by the HMI when the operator selects Punch Tape in the Services screen.
• Archive – a binary container that begins with the %_N_ identifier, embeds a per-block checksum character, and terminates with %%EOF. Archives are produced when the operator selects Archive in Services or when reading out via the PG interface with a binary protocol.

If the PC sends an ASCII Punch-Tape file while the HMI is configured to expect an Archive (or vice-versa), the loader compares the first bytes against the expected magic string. An ASCII file with %_N_MPF1 may superficially match the archive header but will fail the BCC validation on the first block, producing "Die Datei ist kein Archiv". The inverse case – sending a binary archive while the HMI expects ASCII – produces truncated or garbage lines and surfaces as the "Syntax error: please check file/pathname" message.

Layer 2 – Transfer Protocol (RTS/CTS vs Xon/Xoff)

The same Siemens manual lists two supported line protocols for V24 transfer:

• RTS/CTS (hardware handshake) – the default. Uses pins 4 (RTS) and 5 (CTS) of the 25-pin SUB-D connector (X6 on the operator panel front). The HMI raises RTS when its input buffer has space; the PC raises CTS when its output buffer has space. The two control signals throttle the data flow.
• Xon/Xoff (software handshake) – uses DC1 (0x11) and DC3 (0x13) characters embedded in the data stream. The receiver transmits DC1 to resume, DC3 to pause. Pins 4 and 5 are not used for flow control in this mode and must not be looped back, as the handshake is in-band.

If the PC and HMI disagree on which handshake is active, characters are dropped or duplicated, producing the syntax error path described above.

Layer 3 – Serial Framing (Baud, Data, Parity, Stop)

The HMI default and the recommended PC-side settings are listed in the table below. Any drift produces a framing error which the HMI surfaces as either an archive mismatch (Layer 1) or a pathname syntax error (Layer 2 path).

Step-by-Step Resolution

Apply the following procedure in the order given. Do not skip the verification step at the end of each phase.

Step 1 – Confirm the Cable and Connector

1. Use a shielded V24 (RS-232-C) cable, maximum length 15 m at 19200 baud or 5 m at 38400 baud per the EIA-232 standard.
2. Identify the connector on the 840D operator panel front: 25-pin male SUB-D, labelled X6 (or COM1 on PCU 50.3 / PCU 50.5 panels). The PC end is a 9-pin female SUB-D on virtually all industrial PCs built after 2000.
3. Pin-out reference (X6 / PCU 50 COM1):

Cross-over must be applied: pin 2 to pin 3, pin 4 to pin 5, pin 6 to pin 20, pin 7 to pin 7. A null-modem adapter or pre-made Siemens 6FC9341-1HA cable is the field-proven choice.

Step 2 – Configure the HMI Input Screen

1. On the operator panel, navigate to Services → Read in (or the older HMI Advanced menu path Start → Services → V24).
2. Set the following values exactly:

3. If your part programs were previously written as Archive files by an external tool (e.g. SINUTRAIN export, or a third-party CAM post-processor set to "Siemens Archive"), switch the format selector to Archive instead of Punch Tape. The selector is on the same HMI screen, immediately under the protocol field.

Step 3 – Configure the PC Terminal

Configure the terminal program on the PC (Windows-side example, equivalent for Linux stty parameters shown for reference):

Windows COM port settings (Device Manager → Ports → COM1 → Properties → Port Settings):
  Bits per second: 9600
  Data bits:       7
  Parity:          Even
  Stop bits:       1
  Flow control:    Hardware (RTS/CTS)

Linux equivalent:
  stty -F /dev/ttyS0 9600 cs7 parenb -parodd cstopb crtscts -ixon -ixoff raw

Set the terminal program to send the file as raw text with no protocol translation. In Tera Term this is the File → Send file menu with the Binary checkbox off. In Windows HyperTerminal, use Transfer → Send Text File. Do not use Zmodem, Xmodem, Kermit, or Ymodem on the V24 interface of the 840D – these protocols are not implemented on the HMI side and will be rejected as non-archives.

Step 4 – Use the PG Interface as an Alternative

If the V24 path continues to misbehave after the configuration above, the field-proven alternative documented in service practice is to switch the HMI input selector from V24 to PG (programming device interface). The PG interface uses a different framing and protocol stack and is more tolerant of file-format mismatches because the HMI performs auto-detection of Punch Tape vs Archive on the PG channel.

1. On the HMI Services screen, change the top selector from V24 to PG.
2. Re-send the file. The archive error will not appear because the PG path performs header sniffing before format commitment.

Verification Procedure

After applying Steps 1–4, perform the following verification sequence. Each step must pass before the next is attempted.

1. Loopback test: With the cable disconnected, run a serial loopback (pin 2 shorted to pin 3 on the PC end). Send any text from the terminal program; the local echo should show the same bytes. This proves the PC UART and the terminal program are configured.
2. Read-out from NC to PC: On the HMI, run Services → Read out → V24. Select a known-good .MPF file. On the PC, capture the text into a file. Open the captured file in a hex editor; the first bytes must be %_N_MPF... for an Archive, or a plain NC block (e.g. G01 X0 Y0) for Punch Tape.
3. Read-in from PC to NC (round-trip): Rename the existing program on the NC (e.g. MPF1 to MPF1_OLD) so the loader creates a fresh entry. Send the captured file back to the NC. The HMI must accept it and the new program must appear in the program manager with the original name restored.
4. Block-count check: Compare the line count of the file on the PC with the block count reported by the HMI after the transfer. A discrepancy of more than 2 blocks indicates that the line discipline dropped characters – re-check the RTS/CTS wiring or the Xon/Xoff setting.

Troubleshooting Matrix

Format Reference – Punch Tape vs Archive

The two on-the-wire formats are structurally different. Operators must know which their CAM post-processor emits.

Protocol Reference – RTS/CTS vs Xon/Xoff

For the procedure described in the official Siemens manual (Setting V24 in the program manager), leave the protocol at RTS/CTS unless there is a documented reason to switch.

Edge Cases and Field-Proven Caveats

1. PG-vs-V24 selector persistence: The HMI does not remember the last-used interface across a power cycle on all firmware versions. After a cold restart, the selector may default back to V24. After any NCK reset, re-verify the interface selector before re-trying a transfer.
2. Long program names with spaces: The syntax error path is also triggered if the file on the PC contains spaces or non-ASCII characters in the path. Store the file in a path with no spaces and 7-bit ASCII characters only (e.g. C:\NC\MPF1.MPF).
3. CR vs LF line endings: Windows tools often emit CR+LF. The 840D HMI expects LF only. Configure the terminal to translate CR to nothing or to LF, otherwise a stray 0x0D appears in the first block and breaks the archive header check.
4. Touch panel vs keyboard on HMI: On PCU 50.3 panels with touch, the Services menu is reached via the system menu, not via a hard key. The parameter fields are entered with the virtual keyboard.
5. Operator panel vs NCU: The V24 connector discussed here is on the operator panel front (PCU 50 / OP 010 / OP 010C / OP 012 / OP 015 / OP 015A). Do not confuse it with the X122 / X132 interfaces on the NCU, which are fieldbus interfaces, not serial V24.
6. Firmware version sensitivity: On SW 4.5 and later (840D sl), the HMI input screen layout is unchanged but the default for the protocol selector was extended to include "None". Setting the protocol to "None" disables both handshakes and produces intermittent block drops. Always set an explicit protocol.

Commissioning Checklist

1. Confirm V24 cable pin-out against the table above.
2. Open the HMI Services screen, set the interface to V24, and the protocol to RTS/CTS.
3. Set baud 9600, 7 data bits, Even parity, 1 stop bit on the HMI.
4. Set the same values on the PC terminal program. Match the file format (Punch Tape or Archive) to the actual file.
5. Run a loopback test on the PC side.
6. Read out a known-good program from NC to PC. Verify the file content in a hex editor.
7. Rename the original on the NC, then read the same file back in. Verify block count.
8. If Steps 6–7 fail, switch the HMI selector from V24 to PG and retry Steps 6–7.
9. Document the final settings on the machine's commissioning sheet for future operators.