8/9/2010 5:34 PM | |
Joined: 1/28/2009 Last visit: 9/10/2024 Posts: 6849 Rating: (1365) |
Hi Please check the different memory area for a CPU317 in attached photo. As you know PLC is a complicated digital circuit and in the era of nano electronics using capacitors to retain data seems old- fashoined. Best regards Attachmentmemory.zip (255 Downloads) |
8/9/2010 9:06 PM | |
Joined: 9/27/2006 Last visit: 9/19/2024 Posts: 12282 Rating: (2684)
|
Hello Corben; To add a little information on retentivity in S7-300 CPUs, here is an extract from the S7-300 Compact CPUs Technical Specs manual that explains things a bit: 5.1.2 Retentivity of load memory, system memory, and main memory Your CPU is equipped with a maintenance-free retentive memory, i.e. no back-up battery is required for its operation. Due to the retentivity, the content of the retentive memory is retained even during a POWER OFF and restart (warm restart). Retentive data in the load memory Your program in the load memory is always retentive: It is stored on the SIMATIC Micro Memory Card, where it is protected against power failures or memory resets Retentive data in the system memory In your configuration (Properties of CPU, Retentivity tab), specify which part of memory bits, timers and counters should be kept retentive and which of them are to be initialized with "0" on restart (warm restart). The diagnostic buffer, MPI address (and baud rate), and runtime meter data are generally stored in the retentive memory area on the CPU. Retentivity of the MPI address and baud rate ensures that your CPU can continue to communicate, even after a power loss, memory reset, or loss of communication parameters (e.g. due to removal of the SIMATIC Micro Memory Card or deletion of communication parameters). Retentive data in the main memory The contents of retentive DBs are always retentive at restart and POWER ON/OFF. Retentive data blocks can be uploaded to the main memory in accordance with the maximum limit allowed by the main memory. In the case of CPU versions V2.0.12 and higher, non-retentive DBs are also supported. Non-retentive DBs are initialized from the load memory with their initial values at restart or POWER ON/OFF. Non-retentive data blocks and code blocks can be loaded in accordance with the maximum main memory limit. http://support.automation.siemens.com/WW/view/en/12996906 |
Last edited by: dchartier at: 8/9/2010 9:08 PM |
|
8/10/2010 3:36 AM | |
Joined: 1/14/2009 Last visit: 7/19/2024 Posts: 19 Rating: (0) |
HiChartier, I mean version of S7-300 CPUs are V2.0 or later.I'd read the manual before I ask the question here in the forum, the manual didn't tell the time limit that data retained. I'm still confused, if the manual just tells the function is achieved by a NVRAM or by a Capacitor, I'll know whether the time has a limit or not. Thank you and, BR, Corben
|
8/10/2010 7:33 PM | |
Joined: 9/27/2006 Last visit: 9/19/2024 Posts: 12282 Rating: (2684)
|
Hello Corben; If the data is retained in the MMC (newer S7-300 CPUs) there is no limit to the time of retention. It will stay there until the flash-memory is erased or destroyed. If the data is battery-backed, then it seems that some calculations must be used to determine the minimum retention time. The following link is to a FAQ that explains the principles behind this, and lets you down;load a retention calculator for S7-400 CPUs: http://support.automation.siemens.com/WW/view/en/17900782 Hope this helps, Daniel Chartier |
Follow us on