Configuring Retentive Tags on S7-1200 CPU 1214C in TIA Portal

Overview

The Siemens SIMATIC S7-1200 CPU 1214C retains process values across power cycles only for tags that are explicitly marked as retentive in the project. The default TIA Portal project leaves all tags non-retentive, so values written to %MW, %MD, global PLC tags, and Data Block tags are cleared during the STOP-RUN transition and after a power-loss cold start. This reference walks through configuring retentive tags on the CPU 1214C AC/DC/RLY (6ES7214-1AG40-0XB0), resolves the common "greyed-out Retain column" symptom, and provides verification steps, capacity tables, and alternate storage strategies (DB-level Retain attribute, recipe DB, recipe view on SIMATIC Memory Card).

Prerequisites

• Siemens TIA Portal V15 or newer (V17 / V18 recommended for projects using CPU firmware V4.4 or V4.5).
• CPU firmware V4.2 minimum; V4.4 or V4.5 typical in 2023-2024 builds.
• CPU part number 6ES7214-1AG40-0XB0 (SIMATIC S7-1200 CPU 1214C AC 120/230 V / DC 24 V inputs / Relay outputs).
• Project open with the CPU device configured and an online path (PROFINET, PROFIBUS, or serial) to the S7-1200 for the verification step.
• Edit rights for PLC tag table and data block properties (know-how protection on enclosing blocks disabled).

Hardware Identification: 6ES7214-1AG40-0XB0

Refer to the S7-1200 Programmable Controller System Manual (Edition 04/2024) and the catalog entry in the Siemens Industry Mall for full specifications.

Understanding Retentive Memory on the S7-1200

Three memory classes govern value survival across CPU restarts:

1. Non-retentive work memory - cleared on STOP-RUN transition, power-down, and cold restart.
2. Retentive work memory - values survive STOP-RUN transition, warm restart (OB100), and cold restart. The S7-1200 allocates a contiguous byte range beginning at MB 0; the maximum on the 1214C is 10 KB.
3. System-retained memory - certain counters, timers, and diagnostics the firmware retains without explicit user configuration.

Retentivity is decided at compile time. Increasing the retentive byte count consumes the 10 KB budget; if the budget is exceeded, TIA Portal emits a compile error: Retentive memory area too large. Plan the remanence region before declaring tags.

Why the Retain Column Is Greyed-Out

The Retain checkbox in the PLC tag table is disabled under one of the following conditions:

• Tag is mapped to the I, Q, AI, AQ, or PI area. Process I/O cannot be defined as retentive; the operating system overwrites these on every cycle.
• Tag is a member of an optimised Data Block. Retentivity is set inside the DB properties ("Attributes > Retain"), not in the PLC tag table.
• The project's Retain memory byte count is zero. Open CPU properties > Retain memory and set a non-zero value.
• PLC user program has know-how protection set on the enclosing OB/FC/FB with write protection. Remove protection, retry, then re-apply protection.
• Toolbar filter "Hide non-retentive tags" is active. Clear the filter icon in the PLC tag table toolbar.
• Target device differs from the CPU in the project. The S7-1200 retention model is different from the S7-1500 behaviour - check the slot's module selection.

Configuring Retentive Tags Step-by-Step

Step 1 - Allocate Retentive Memory Bytes

1. In the project tree, right-click the S7-1200 CPU (for example, PLC_1 [CPU 1214C AC/DC/RLY]) and choose Properties.
2. Switch to the navigation entry Retain memory (or Retention on TIA V17+ for firmware 4.4 targets).
3. Set Retentive memory bytes. For example, enter 100 to make MB 0 .. MB 99 retentive.
4. Click OK, recompile (Project > Compile > Software (rebuild all)), then download "Hardware and Software (full)" to the CPU.

Step 2 - Mark Tags as Retentive in the PLC Tag Table

1. Open PLC tags > Default tag table (or your custom tag table).
2. Add a tag: Name = ProductionCount, Data type = Int, Address = %MW100.
3. Place a tick in the Retain column for that row. If grey, see the reasons in the previous section.
4. Recompile and download to the CPU.

Per the TIA Portal Information System, Help topic "Setting the retentive behavior of PLC tags": "You set the retentivity for PLC tags in the PLC tag table for the S7-1200/S7-1500 CPU series. You can recognize the retentivity setting of a tag by the check mark set in the 'Retain' column of the PLC tag table." Reference: Siemens TIA Portal Help - PLC tag retention (KB entry).

Step 3 - Power-Cycle Verification

1. Place the CPU in RUN. Use a watch table to write a value into MW 100: Modify value = 1234, confirm applied.
2. Disconnect the AC supply for >= 5 seconds (longer for cold-restart test).
3. Reapply power; wait for the CPU RUN LED solid green.
4. Reconnect with TIA Portal; read MW 100. Expected value = 1234. If 0, the retentive range was not allocated or the download skipped the remanence table.

Alternative - Retentive Data Block Tags

Siemens' preferred long-term storage on the S7-1200 is a dedicated Data Block with the Retain attribute toggled at the block level; every static tag inside that DB then inherits retentive behaviour.

Creating a Retention Data Block

1. Project tree > Program blocks > Add new block > Data block. Name it RecipeDB.
2. Select type Global DB. Use optimised block access for modern S7-1200 / S7-1500 use cases; select non-optimised (classic) only if the HMI or third-party device needs absolute %DBW addressing.
3. Open DB properties > Attributes. Tick Retain under Retain attribute.
4. Declare static variables:

5. Compile and download the DB block individually (Program blocks > Download to device > Software (only changes)).

Programmatic access from an OB or FB in SCL: "RecipeDB".Counter := "RecipeDB".Counter + 1;
In LAD/FBD ladder (counter example): L "RecipeDB".Counter / + 1 / T "RecipeDB".Counter

M Retain vs DB Retain vs RecipeDB Comparison

RecipeDB and Recipe View (Persistent Storage on Memory Card)

For long-term persistence across firmware updates, CPU replacements, or hot standby CPU swaps, use a RecipeDB with a PLC data type of Recipe. Combine it with:

• The HMI Recipe View object in WinCC / TIA Portal HMI engineering.
• Recipe functions in the user program using RDP (Read data of recipe) and WRP (Write recipe to recipe DB) system instructions.
• File-system export to the SIMATIC Memory Card (recipe directory /Recipes on the SD card).

Recipe data resides in load memory, not in work memory, so it persists even after a complete firmware update. Reference: S7-1200 Recipes in TIA Portal (Application Note).

Memory Map Reference (CPU 1214C AC/DC/RLY)

Troubleshooting Matrix

Verification Procedure

1. Online: Connect to the CPU (Online > Go online) and place the mode selector at RUN.
2. Modify: Open a Watch Table and force %MW100 to 1234 via "Modify now".
3. Power-down: Use the main breaker to drop AC supply for at least 10 seconds.
4. Power-up: Restore AC supply. Wait for LED pattern RUN solid green (no MAINT/ERROR).
5. Read-back: Go online again, monitor %MW100. Expected value 1234.
6. Data block equivalent: Repeat for "RecipeDB".Counter. Both should hold value.

Best Practices and Engineering Notes

• Allocate retentive memory only for state variables: counters, totalisers, calibration offsets, setpoints. Avoid using it for transient buffers or pulse trains.
• Reserve recipes and configuration sets for the Memory Card - not for in-CPU work memory - if the machine must survive CPU swap.
• After any retentive-range change, always download Hardware and Software (full); otherwise the remanence table does not update.
• Document retentive and non-retentive regions in the program's header comment block so commissioning engineers can predict cold-restart behaviour.
• Before firmware updates, save the recipe directory to the SIMATIC Memory Card and a backup file to FAT/exFAT USB storage.
• For multi-CPU redundancy setups, recipe data on a shared Memory Card is the supported path for state synchronisation.

Related References (Siemens Documentation)

• S7-1200 Programmable Controller - System Manual
• TIA Portal Help - Setting retentive behaviour of PLC tags
• S7-1200 Application Note - Recipes via TIA Portal
• Siemens Industry Mall - 6ES7214-1AG40-0XB0 catalog entry

FAQ