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S7-300 CPU 31x -- Product information -- Background and system information
What are the differences between OPEN MODBUS / TCP Redundant V1 and OPEN MODBUS / TCP Redundant V2?
What is the difference between "normal routing" and data record routing?
Which SIMATIC S7-300/S7-400 modules support the NTP time-of-day message and how do you activate this kind of time synchronization?
Which manufacturer ID, in other words OUI (Organizationally Unique Identifier), does SIEMENS AG use for the MAC addresses of network-compatible devices?
What should you watch out for when using the alarm numbering procedure?
Which IO controllers and IO devices support the following functions: IRT, prioritized startup, MRP, PROFIenergy, Shared device, I device and clock-synchronized mode?
What is the maximum number of parameters that can be assigned to an FC and FB in the S7-300 CPU?
Which types of connection/protocols do the S7-300/400 CPUs and the CPs support by default?
Which PROFINET nodes support automatic commissioning (device replacement without interchangeable medium) in the case of topological configuration and device replacement without topological configuration?
Which PROFINET nodes support the extended PN diagnostics and what do you have to configure?
Why is only a warm start available for S7-300?
Which SIMATIC S7 modules support the "Direct Data Exchange" function (internode communication)?
Which entries deal with consistent data in conjunction with distributed I/O?
What properties, advantages and special features does the S7 Basis Communication offer?
What properties, advantages and special features does the global data communication offer?
What is the connection between subnet masks and IP addresses with regard to subnetting and supernetting (Classless Inter Domain Routing CIDR)?
Which modules support the S7 routing function?
How can you obtain an overview of the memory concept of SIMATIC S7-300 CPUs and C7 devices?
Retentivity behavior of S7-300 CPU 31x and complete devices C7-6xx with MMC
Status of the run-time meter after overall reset
Why does the retentivity behavior of the S7-300 CPUs and C7 devices without MMC (Micro Memory Card) influence the contents of the variables?
Local data addressing with S7-300 / S7 400
S7 300 run-time meter doesn't give any value
C7 6xx -- Product information -- Background and system information
Which external storage media can you use with the SIMATIC panels and which memory card interfaces do they have?
The C7 6xx complete devices are to be discontinued in October 2010 – what are their successors?
How do you display ALARM_S or ALARM_D messages with process values (so-called associated values) on a WinCC flexible operator panel?
Which connector cables are available for connecting to SIMATIC Panels?
How many connection resources can be managed by the C7-CPU or the C7-OP?
Which GSD file do you need for a C7 Complete Device?
Which software do you need for the C7-621 module (with integrated AS interface master)?
How can you obtain an overview of the memory concept of SIMATIC S7-300 CPUs and C7 devices?
Why does the retentivity behavior of the S7-300 CPUs and C7 devices without MMC (Micro Memory Card) influence the contents of the variables?
Retentivity behavior of S7-300 CPU 31x and complete devices C7-6xx with MMC
Overview of components integrated in a C7 complete system
Why does the retentivity behavior of the S7-300 CPUs and C7 devices without MMC (Micro Memory Card) influence the contents of the variables?
Part number:

 
Description:
The retentivity behavior of the separate variables is important for developers when creating programs. Developers usually have variables in their programs, whose contents are to be retained even during POWER OFF (retentive) and other variables that then have to be reset to a defined value (non-retentive). In SIMATIC STEP 7 developers can therefore configure retentive address areas for data, markers, S7 timers and S7 counters which they can then use for retentive variables. This entry describes the retentivity behavior of the address areas of SIMATIC S7-300 CPUs and C7 devices without Micro Memory Card (MMC).  The retentivity behavior of the address areas is described for the POWER OFF/ON change of status, the STOP/RUN operating mode and for overall reset.
This entry does not refer to the retentivity behavior with the CPU S7-318. The retentivity behavior with CPU S7 318-2 is described in Entry ID: 23596519.

The entry is divided into the following topics:

Conditions of the retentivity behavior

The retentivity behavior of address areas with CPUs without MMC depends on:

  • The CPU.
  • The use of battery and memory card (MC).
  • The parameterization in the HW Configuration.

Note:
Not all CPUs and C7 devices can be equipped with battery, memory card or micro memory card.

Program blocks and data blocks at POWER OFF/ON

Without buffer battery:

  • If the program and data blocks in the main memory are not buffered by a battery, then they are lost after POWER OFF/ON. However, the values in the retentive address areas - as configured in the hardware configuration (see Table 02) - are retained. After POWER OFF/ON the runtime-relevant data blocks and program blocks are reloaded from the FLASH memory card (if slotted) or from the internal FLASH load memory (if available) into the main memory, whereby the values for data block elements declared as retentive are taken from the retentive memory.
    In the case of non-retentive data blocks the current values are reloaded from the load memory. If there are no current values in these data blocks in the load memory, then the initial values are loaded from the load memory.
  • Data blocks and program blocks in the internal RAM load memory are lost at POWER OFF/ON.

With buffer battery:

  • If you use a battery, the program and all the data blocks are buffered in the main memory. They are retained after POWER OFF/ON.
  • If a buffer battery is implement, all the data blocks are retentive.

With rechargeable battery:

  • When using a rechargeable battery, only the time is buffered.
  • However, the values in the retentive address areas - as configured in the hardware configuration (see Table 02) - are retained.

Data, markers, S7 timers and S7 counters at POWER OFF/ON

The following points apply for markers, S7 timers and S7 counters at POWER OFF/ON:

  • If a retentivity area has been parameterized for markers, S7 timers and S7 counters in the HW Configuration (see Table 02), the values in the address areas concerned are retained.
  • If a retentivity area has been parameterized for data blocks in the HW Configuration (see Table 02), then the data save at POWER OFF is transferred again to the data block areas concerned.

Program blocks and data blocks in STOP/RUN operating mode

The following points apply for program blocks and data blocks in the STOP/RUN operating mode:

  • The program blocks and data blocks are retained in the main memory and are not reloaded from the load memory.
  • There are no changes to the contents of the data blocks. All data blocks are retentive.

Data, markers, timers and counters in STOP/RUN operating mode

All the markers, S7 timers and S7 counters entered in the retentivity area in the HW Configuration (Fig. 03) are retained in the STOP/RUN operating mode. All other markers, S7 timers and S7 counters are reset.

Data, markers, S7 timers and S7 counters at overall reset

All markers, S7 timers and S7 counters are reset at overall reset. In the case of data blocks the current values are reloaded from the load memory (FLASH memory card or internal FLASH). If there are no current values in these data blocks in the load memory, then the initial values are loaded from the load memory.

Information on the elapsed time counter is available in the Entry ID: 2804630.

Important:
If you wish to communicate with the CPU from your PG/PC after the overall reset, the only option you have for setting up this communication is via the MPI or MPI/DP interface.

Comparison of overall reset and "POWER OFF/ON without buffer battery and without memory card" with S7-300 CPUs and with C7 devices without MMC

In the case of "POWER OFF/ON without buffer battery and without memory card" the retentive areas remain unaffected. If the program is reloaded in this case, then it works with the old values from the retentive area. By default these are the first 8 counters, for example. This can lead to dangerous plant statuses if you don't take this into account. The effects of overall reset and "POWER OFF/ON without buffer battery and without memory card" are compared in Table 01. 

Recommendation:
After a "POWER OFF/ON without buffer battery and without memory card" always do an overall reset.
 
  Overall reset "POWER OFF/ON without buffer battery and without memory card"
Changed
  • The hardware configuration is deleted.

  • The program is deleted.

  • The retentivity areas are deleted.

  • The hardware configuration is deleted.

  • The program is deleted.

Unchanged
  • The diagnostics buffer.

  • The protection level set.

  • The parameters of the MPI interface (MPI address, ...)

  • The retentivity areas are not deleted.
  • The diagnostics buffer.
  • The protection level set.

  • The parameters of the MPI interface (MPI address, ...)

Table 01

How to configure retentive address areas in STEP 7

The following Table 02 describes how to proceed to configure retentive address areas in an S7-300 CPU without MMC.
 
No. Procedure
1 Open the Hardware Configuration of your S7-300 station. Double-click on the icon of your CPU --> The "Properties - CPU 31x ..." window opens.


Fig. 01
 

2 Select the "Retentive Memory" tab.


Fig. 02
 

3 In the "Retentive Memory" tab, in the "Retentivity" field you can configure the retentive address areas for:
  • Markers
  • S7 timers
  • S7 counters

In the "Areas" field you can also configure the retentive areas in data blocks.


Fig. 03
 

Warning:
Please make sure that your data blocks defined as retentive are available in the CPU and are not too short.
Likewise the data blocks must not have the "Unlinked" property. Otherwise the data blocks are only loaded into the load memory.

4 After defining the desired retentive areas you can quit the CPU Properties dialog via "OK" or make changes in other tabs.
Table 02

Warning:
Please note that in the meantime C7 devices without MMC have been discontinued. An MMC must be used with all the current C7 devices (C7-613, C7-635 and C7-636).

 Entry ID:598803   Date:2006-08-28 
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