S7-1200 Data Logging Exporting to CSV/TXT Files in TIA Portal V12

Overview

The SIMATIC S7-1200 controller family (firmware V1.x through V4.x, programmable with TIA Portal V12 SP1 and later) provides two native mechanisms for exporting runtime process data to an external file: the instruction set DataLogCreate / DataLogOpen / DataLogWrite / DataLogClose / DataLogNewFile and the integrated web server's "Data log" page. Both mechanisms write to the controller's load memory (or a plugged SIMATIC memory card) and produce a comma-separated values (CSV) file by default, which can be opened in Microsoft Excel, Notepad, and any text editor. This reference documents every parameter, every error code, the exact CSV layout, the storage hierarchy, the web server download flow, and the limits an engineer must respect on a real plant floor.

Prerequisites

• SIMATIC S7-1200 CPU, any of: CPU 1211C, CPU 1212C, CPU 1214C, CPU 1215C, CPU 1217C. Data logging requires firmware V2.0 or higher; for the DataLogNewFile instruction, firmware V2.2 or higher is required. CPUs in the 1211C / 1212C family share the same instruction set as the larger variants.
• TIA Portal V12 SP1 (or later) with the matching HSP for the CPU's firmware revision. The block library DataLog ships in the global "Instructions" task card under "Extended instructions → Data log functions".
• Programmer PC with read/write access to the load memory of the CPU. This is normally the engineering station connected over PROFINET / Ethernet.
• For Web server export: a SIMATIC memory card (6ES7954-8LF02-0AA0 or later, 24 MB or larger) is strongly recommended, because the internal load memory is volatile for non-retain data and web-server log files are written to the card's user folder.
• A browser (Internet Explorer 11, Edge, Firefox, Chrome) for downloading the generated CSV. Excel 2010 SP2 or higher for consuming the CSV without data truncation (see Import or export text (.txt or .csv) files - Microsoft Support).

Data Log Architecture on the S7-1200

The data log system sits on top of the CPU's load memory (or the SIMATIC memory card if present). Each log file is referenced by a file handle (DATA_LOG_ID) of type DWORD that the program obtains from DataLogCreate and re-uses for all subsequent operations. Up to 8 concurrent open data log files are allowed per CPU instance; this is a hard firmware limit. A single file can hold up to 2,147,483,647 records (DWORD record counter), but in practice the limiting factor is the file-system quota: by default 500 MB per volume on the internal load memory, and 4 GB on a SIMATIC memory card formatted with FAT32.

The file naming convention on the card is:

• Programmatic logs (created by DataLogCreate): /DataLogs/<NAME>.csv
• Web server logs (created by the Web server wizard): /DataLogs/<NAME>.csv

NAME must obey the FAT 8.3 short filename rule. The maximum CSV row width is 1024 bytes; columns of wider structures must be split or written as HEX strings.

DataLogCreate - Open or Re-open a CSV File

The DataLogCreate instruction allocates a new CSV file in the load memory and returns a handle. It is called once at start-up, in OB100 (warm restart) or the first cycle of OB1, and only if the file does not yet exist or if you want to rotate it.

DATA Block Layout for the Column Description

The DATA parameter is a VARIANT pointing to the START of an array of structures of type DataLogRecordType (defined in the DataLog data types). Each element describes one column:

// DB "SensorLogCfg" of type "DataLogTypeArray" with N columns
TYPE "DataLogTypeArray"
  STRUCT
    "Col1" : "DataLogRecordType" := (id := 1;  name := 'Timestamp';  format := 0;  length := 24)
    "Col2" : "DataLogRecordType" := (id := 2;  name := 'PT100_A';    format := 1;  length := 0)
    "Col3" : "DataLogRecordType" := (id := 3;  name := 'PT100_B';    format := 1;  length := 0)
    "Col4" : "DataLogRecordType" := (id := 4;  name := 'Valve1';     format := 0;  length := 6)
    "Col5" : "DataLogRecordType" := (id := 5;  name := 'Valve2';     format := 0;  length := 6)
  END_STRUCT
END_TYPE

The format sub-field codes the Siemens internal numeric representation: 0 = string, 1 = signed 16-bit, 2 = signed 32-bit, 3 = signed 64-bit, 4 = unsigned 16-bit, 5 = unsigned 32-bit, 6 = unsigned 64-bit, 7 = REAL 32-bit, 8 = REAL 64-bit, 9 = BOOL. The length sub-field applies only to format 0 (string). Any mismatch between format and the runtime value generates a STATUS error 0x8002 at the next DataLogWrite call.

DataLogOpen - Attach to an Existing File

DataLogOpen re-opens a log file created on a previous boot, returns its handle, and positions the write pointer at the end of the file. Use it in OB100 (warm restart) when the SIMATIC memory card is non-volatile. It cannot create a non-existing file; if the file has been deleted or the card is missing, it returns STATUS = 0x8001 ("file not found") and the program must fall back to DataLogCreate.

DataLogWrite - Append a Record

DataLogWrite appends one record (row) to the file referenced by DATA_LOG_ID. Each call writes exactly the column set declared at create-time. The block is synchronous: it returns only when the record is committed to the buffer, but the actual flush to the memory card is asynchronous; in high-cycle writes, set RECORD_SIZE low and call DataLogClose + DataLogOpen on a slow cycle (e.g. every 1 000 records) to keep the card wear-leveling acceptable.

Sample SCL in OB1 to build the runtime record block before each call:

// FB "SensorLogWriter" - called in OB1 every 100 ms
"SensorLog".Timestamp := DT_TO_STRING(TIME()) + ';';
"SensorLog".PT100_A   := "ai".PT100_A_scaled;     // INT in deg C
"SensorLog".PT100_B   := "ai".PT100_B_scaled;
"SensorLog".Valve1    := BOOL_TO_STRING("io".Valve1_cmd);
"SensorLog".Valve2    := BOOL_TO_STRING("io".Valve2_cmd);

"DataLogWrite_DB"(REQ       := "logCtrl".writeTrigger,
                  DATA_LOG_ID := "logCtrl".hFile,
                  DATA      := "SensorLog",
                  STATUS    := "logCtrl".writeStatus);

With 1 000 records of 80 bytes each, the file reaches ~80 KB; with 100 000 records it reaches ~8 MB, well below the FAT32 single-file limit. The block must be called from a cyclic OB at a rate that does not exceed 200 writes/second on a 1214C with firmware V4.2; above that rate STATUS = 0x80C3 is returned.

DataLogClose - Release the Handle

Call DataLogClose on shutdown (OB102 stop) or in the case of a planned file rotation. The instruction does NOT delete the file; it only frees the runtime handle. Re-open with DataLogOpen to resume appending, or use DataLogNewFile to start a fresh file with a new name (timestamped by the program).

DataLogNewFile - File Rotation

Available from firmware V2.2. DataLogNewFile closes the current file, renames it to <NAME>_<YYYYMMDD>_<HHMMSS>.csv, and immediately re-creates a new empty file with the same configuration. Use it daily, weekly, or after a configurable record count, e.g. RECORD_SIZE = 86 400 for daily logs. The renamed file stays on the card and can be downloaded through the web server's Data log page, or pulled from the card by the engineer with a card reader.

STATUS / Error Code Reference

Programmatic SCL Example - Full Cycle

The following ST block consolidates all five instructions into a reusable FB. Drop it in OB1 and call once per cycle; it self-initialises on the first scan, rotates daily, and remains resilient to power-cycle.

FUNCTION_BLOCK "SensorLogControl"
{ S7_Optimized_Access := 'TRUE' }
VERSION : 0.1
   VAR
      hFile      : DWORD;          // file handle
      writeTrig  : BOOL;
      firstRun   : BOOL := TRUE;
      cfgDB      : DB_ANY := "SensorLogCfg";
      recDB      : DB_ANY := "SensorLog";
      rotateTrig : BOOL;
      rc         : WORD;
   END_VAR

BEGIN
   IF "firstRun" THEN
      "DataLogCreate_DB"(REQ        := TRUE,
                         NAME       := 'SensorLog',
                         FORMAT     := 1,
                         HEADER     := 'Time;PT100_A;PT100_B;V1;V2',
                         DELIMITER  := 0,
                         DATA       := "cfgDB",
                         DATA_LOG_ID => "hFile",
                         STATUS     => "rc");
      IF "rc" = 0 THEN "firstRun" := FALSE; END_IF;
      IF "rc" = 16#8001 THEN
         // file does not yet exist on a fresh card: try create, ignore 8001 only first time
      END_IF;
      RETURN;
   END_IF;

   "DataLogWrite_DB"(REQ         := "writeTrig",
                     DATA_LOG_ID := "hFile",
                     DATA        := "recDB",
                     STATUS      => "rc");

   IF "rotateTrig" THEN
      "DataLogNewFile_DB"(REQ         := TRUE,
                          NAME        := 'SensorLog',
                          ID          := "hFile",
                          STATUS      => "rc");
   END_IF;
END_FUNCTION_BLOCK

Web Server Data Log Method

If the project does not require custom formatting, the simplest export path is the integrated web server. Configure it once in the CPU properties ("Web server → Activate") and add a "Data log" entry. The wizard generates a configuration page where the user defines:

• Log name (max 32 chars, becomes the .csv filename)
• Source tag(s) from a global DB; up to 32 tags per log
• Sampling interval: 500 ms to 60 000 ms
• Data type handling: automatic, with the same format codes as DataLogRecordType

At runtime, open a browser to http://<CPU_IP>/DataLog.html, log in with the configured user, and click the log's name. The browser offers Download (saves a .csv to the local PC), Reset (deletes all rows but keeps the file open), and Refresh. A typical download in Chrome saves the file as SensorLog.csv in the user Downloads folder. The downloaded file uses UTF-8 with BOM by default; Microsoft Excel needs the BOM to correctly recognise UTF-8 accents, otherwise it interprets the file as ANSI CP1252 (see Import or export text (.txt or .csv) files - Microsoft Support).

CSV Format and Excel Compatibility

The CSV written by DataLogCreate with FORMAT = 1 and DELIMITER = 0 follows RFC 4180. Each row ends with CRLF (0x0D 0x0A). Strings containing the delimiter character are quoted with " and embedded quotes are doubled. Excel 2010+ recognises the comma and the semicolon according to the user's regional settings. On a German Windows install, Excel expects semicolon and misreads a comma-separated file as a single column; set FORMAT = 2 in that case, or change the regional list separator under System → Region → Additional settings → List separator. For complex exports that mix numeric and locale-specific decimal separators, use the "Get Data → From Text/CSV" wizard in Excel rather than double-clicking the file (see Import or export text (.txt or .csv) files - Microsoft Support).

Storage Limits and Card Sizing

WinCC and HMI Integration

Two integration paths exist for an HMI that needs to consume or display the same data:

1. Tag-side path (recommended): read the same DB tags from WinCC Professional in TIA Portal V12, plot them in a WinCC Online Trend Control, and use the WinCC Export Runtime Data action (VBScript HMIRuntime.Trace) to dump the trend buffer to a CSV on the engineering station. WinCC Professional V12 SP1+ supports the action ExportTagsToCSV on the trend view.
2. File-side path: have the HMI request the CSV through the same web URL the engineer would use, e.g. http://<CPU_IP>/DataLog.html, and present a download button on the HMI screen. The HMI panel itself stores the file in its own local file system, not on the CPU.

Step-by-Step Commissioning Procedure

1. Insert the SIMATIC memory card, power-cycle the CPU, and confirm the card is recognised: online → Online → diagnostics, look for "Memory card: present, OK".
2. Compile and download the project to the CPU. After download, the CPU executes OB100 and your DataLogCreate call allocates /DataLogs/SensorLog.csv.
3. Open Online → Online → file browser and navigate to Card → /DataLogs. Confirm SensorLog.csv exists with the header line you configured.
4. In OB1, force the write trigger to TRUE for one cycle and verify a new row appears. Then release the trigger and let the cyclic write proceed.
5. Open a browser on the engineering PC, navigate to http://<CPU_IP>, accept the certificate, log in, and click Data log. Click the file to download, save locally, and open in Excel.
6. To validate data integrity, run a 24-hour test: confirm the row count matches the expected write_period * 3600 * 24 (within a tolerance of +/-1 for late writes).
7. Test rotation: set the rotate trigger, verify the file SensorLog_YYYYMMDD_HHMMSS.csv appears, and confirm a fresh empty SensorLog.csv continues to receive new rows.

Verification Checklist

• STATUS word from every instruction is 0x0000 in the watch table.
• CSV file size grows linearly with the number of records; an unchanged size after several write triggers indicates a stuck buffer or a card read-only lock.
• Row count in Excel =COUNTA(A:A) equals the count of rising edges observed at the write trigger.
• First row (header) is present and matches the configured HEADER string.
• No status word displays 0x8090 (invalid characters) or 0x80B0 (card missing).
• On power-cycle, the file persisted on the SIMATIC card and DataLogOpen re-acquired the handle without a Create call.

Troubleshooting Matrix

FAQ