C135 PCS 7 (PCS7)
6C
6 Cielo Ciencia y Tecnología
·Publicada en C135 PCS 7 (PCS7)

Sizing Memory Cards and Load Memory for S7-400 Automation Stations in PCS 7

Sizing Memory Cards and Load Memory for S7-400 Automation Stations in PCS 7

A 1 MB memory card is not sufficient for standard SIMATIC PCS 7 automation stations. In PCS 7, S7-400 controllers require external memory cards to hold the compiled load memory, including CFC instances, SFC state logic, system data blocks (SDBs), and Advanced Process Library (APL) drivers. Siemens Catalog ST PCS 7 recommends a minimum of 2 MB RAM for entry-level stations (up to 100 Process Objects), and 4 MB to 16 MB RAM or Flash EPROM for typical industrial applications (200 to 1,000+ Process Objects). Note that S7-400 CPUs use standard full-sized PCMCIA memory cards, not SIMATIC Micro Memory Cards (MMCs).

Table of Contents

Executive Summary

When sizing SIMATIC S7-400 automation stations for SIMATIC PCS 7, engineers must distinguish between integrated CPU work memory, external load memory cards, and Process Object (AS RT PO) software runtime licenses. Unlike standard SIMATIC S7-300 or S7-1500 controllers that utilize Micro Memory Cards (MMCs), S7-400 CPUs require proprietary full-sized PCMCIA memory cards. Because PCS 7 generates substantial overhead—including CFC cross-references, diagnostic blocks, and APL driver structures—a 1 MB card is incapable of holding a typical multi-chart program. This technical guide details the memory sizing rules, compares RAM and Flash technologies, and establishes verified engineering criteria for controller procurement.

S7-400 Memory Architecture: Work Memory vs Load Memory

The memory architecture of an S7-400 CPU (such as CPU 414-3, 416-2, or 417-4) is partitioned into three distinct areas:

  • Integrated Work Memory: High-speed internal execution memory divided equally into Code Work Memory and Data Work Memory. Work memory holds the operational machine code and instance data during cyclic program execution. Work memory capacity is fixed in the CPU hardware and cannot be expanded by external memory cards.
  • Load Memory: Non-cyclic storage containing executable blocks (OBs, FBs, FCs, DBs) and system data blocks (SDBs). Although classic S7-400 CPUs provide a small integrated load memory (typically 256 KB to 1 MB), PCS 7 projects require an external memory card inserted into the CPU slot to expand load memory.
  • System Memory: Contains internal bit memories (M), timers (T), counters (C), I/O process image partitions (PAE/PAA), and diagnostic buffer records.

Memory Card Selection: RAM vs Flash EPROM

When ordering external memory cards for classic S7-400 automation stations, two technology types are available:

  1. RAM Memory Cards: Allow direct online program changes, delta downloads, and online CFC debugging without stopping the controller. However, RAM cards are volatile and require a functional backup battery in the rack power supply module (e.g., PS 407 or PS 405) to preserve the program during power failures.
  2. Flash EPROM Cards: Provide non-volatile storage that retains program logic indefinitely without battery backup. However, transferring changes to Flash requires executing 'Copy RAM to ROM' via SIMATIC Manager, which requires placing the CPU in STOP mode. Consequently, Flash cards are unsuitable for continuous process automation requiring online delta downloads.

Sizing Guidelines by Process Object Count

In PCS 7, compiled code volume correlates directly with Process Object (PO) count and library complexity. A single technological block (such as MotL or VlvL) combined with its associated channel drivers (Pcs7DiIn, Pcs7DiOu) and diagnostic blocks (OB_DIAG1, MOD_D1) consumes between 1.5 KB and 4.0 KB of load memory.

According to Siemens Catalog ST PCS 7:
* Minimal systems (~100 POs): Minimum 2 MB RAM card.
* Small systems (~200-300 POs): Minimum 4 MB RAM card.
* Medium systems (~500-800 POs): Minimum 8 MB RAM card.
* Large systems (1,000+ POs): Minimum 16 MB or 64 MB RAM card.

Procuring a 1 MB card creates an immediate bottleneck during initial project compilation, resulting in compiler error 'Download not possible: Load memory full'.

S7-400 Memory Sizing and Card Specifications

The following table provides verified engineering specifications and typical capacity recommendations for S7-400 memory cards in SIMATIC PCS 7:

Memory Card TypePhysical CapacityVolatility & Battery RequirementOnline Delta Download SupportRecommended Application Scope in PCS 7RAM Card2 MBVolatile (Requires PS 407/405 Battery)Supported (CFC Changes Only)Entry-level automation stations (~100 POs)RAM Card4 MBVolatile (Requires PS 407/405 Battery)Supported (CFC Changes Only)Small process units (150 to 300 POs)RAM Card8 MBVolatile (Requires PS 407/405 Battery)Supported (CFC Changes Only)Standard industrial units (300 to 800 POs)RAM Card16 MBVolatile (Requires PS 407/405 Battery)Supported (CFC Changes Only)Large automation stations (800 to 1,500 POs)RAM Card64 MBVolatile (Requires PS 407/405 Battery)Supported (CFC Changes Only)Maximum configuration stations (1,500 to 2,000+ POs)Flash EPROM Card4 MB to 64 MBNon-volatile (No Battery Needed)Not Supported (Requires STOP for RAM-to-ROM)Batch archive / Standalone non-critical units

Step-by-Step Memory Calculation and Verification Procedure

Method 1: Determining Exact Memory Consumption in SIMATIC Manager

  1. Open the PCS 7 project in SIMATIC Manager.
  2. Open the CFC editor and navigate to Chart > Compile > Changes Only (or perform a full chart compilation if testing new hardware).
  3. In the compilation log window, note the total generated code size and data size.
  4. Select the target CPU in SIMATIC Manager and click PLC > Module Information.
  5. Navigate to the Memory tab to view the live allocation of Work Memory (Code and Data) and Load Memory (RAM/ROM).
  6. Verify that Load Memory utilization does not exceed 70% to ensure sufficient reserve for future online delta downloads.

Method 2: Verifying Battery Backup for RAM Cards

  1. Inspect the rack Power Supply module (e.g., PS 407 10A).
  2. Confirm that two functional lithium backup batteries (3.6V AA) are inserted and the battery switch is set to 1 BATT or 2 BATT.
  3. Confirm that the BAF (Battery Fault) LED on the power supply module is unlit.
  4. In SIMATIC Manager, check the diagnostic buffer to verify absence of battery failure events.

Verification

To verify adequate memory configuration in the engineering environment:

  1. Compilation Check: Perform a full compilation of all CFC charts via Chart > Compile > Entire Program. Verify that the compilation finishes with 0 errors and no memory overflow warnings.
  2. Online Download Test: Perform a delta download via PLC > Download Changes. Confirm that the download completes smoothly without prompting for CPU STOP mode.
  3. Online Memory Diagnostics: Open PLC > Module Information > Memory. Confirm that external load memory reflects the installed card capacity (e.g., 4,194,304 bytes for a 4 MB card) and that free load memory remains above 30%.

Limitations and Operational Precautions

  • Form Factor Incompatibility: Classic S7-400 CPUs do not accept SIMATIC Micro Memory Cards (MMCs) used in S7-300 or ET 200S CPUs. Attempting to force an MMC or third-party PCMCIA card will cause physical damage.
  • AS 410 Distinction: Modern SIMATIC PCS 7 systems utilizing CPU 410-5H do not use standard RAM cards. Instead, CPU 410-5H utilizes a proprietary System Expansion Card (SEC) that governs licensed Process Object capacity, while load and work memory are permanently integrated into the CPU hardware.
  • Battery Maintenance: For all classic S7-400 systems using RAM memory cards, backup batteries must be replaced during scheduled maintenance (typically every 1 to 2 years) while the rack is powered on.
  • Commercial Procurement Disclaimer: Always validate final memory card selection, part numbers, and hardware compatibility against the latest Siemens ST PCS 7 catalog and an authorized Siemens distributor quotation.

Engineer FAQ

Can I use an S7-300 MMC card in an S7-400 CPU slot?

No. S7-300 controllers use small Micro Memory Cards (MMC), whereas S7-400 controllers utilize full-size PCMCIA-format Memory Cards. They are physically and electrically incompatible.

What happens to an S7-400 RAM card if the rack power supply loses power and batteries are dead?

Because RAM is volatile, the complete load memory program is lost. Upon power restoration, the CPU enters STOP mode with a memory reset request (STOP LED flashing slowly).

Does adding an external RAM card expand the CPU Work Memory?

No. External memory cards expand only the Load Memory. Work memory is hardwired internal CPU RAM and cannot be increased by adding an external card.

Technical References

Related Articles

Related Tags

  • https://industrialautomation.net/search?query=simatic-pcs7
  • https://industrialautomation.net/search?query=s7-400
  • https://industrialautomation.net/search?query=hardware-sizing
  • https://industrialautomation.net/search?query=load-memory
6 respuestas