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TP170A to CPU226 memory storage problem

Created by: NeilHornby at: 2/24/2006 1:24 PM (4 Replies)

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2/24/2006 1:24 PM	Rate (0)
NeilHornby Posts: 2 Rating: (0)	Hi there We have a problem on a machine which is controlled by a S7 226CPU unit with a 256k eprom. The machine interface is a TP170A screen. Previously, parameters saved on the screen would be stored and available when the machine was powered off. Now however when a power off occurs, the parameters are lost andrandom numbers were displayed instead. When the values are put back in once more the machine works fine, controlled by these parameters. The machine was powered off and the CPU Eprom replaced, however the saved values are still lost, butinstead of random numbers, zero values are displayed on the screen. There are only half a dozen values to input and the machine/program is working fine - but we really need to keep the values saved in the long term. Any ideas ?? Many Thanks Neil
NeilHornby Posts: 2 Rating: (0)
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2/24/2006 4:56 PM	Rate (0)
NeilHornby Posts: 2 Rating: (0)	Update - I have put the original Eprom back into the CPU and (as per the original fault) on power off/on the TP170a is displaying random values. Put the replacement Eprom back in and once again the TP170a is displaying zero values. Both scenarios are therefore displaying different but consistent problems, and although the values are stored initially they are lost on power down
NeilHornby Posts: 2 Rating: (0)
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3/29/2006 5:25 AM	Rate (1)
Mojo Bronze Member Joined: 3/27/2006 Last visit: 10/11/2024 Posts: 90 Rating: (13)	Greetings. I can tell you what works for me based on my experience with the S7-200 cpu family. On my S7-200 projects I have several steps to ensure data integrity as well as safe operation of the machine. ================================================= First - an explanation of the S7-200 memory as I understand it. Corrections/comments are welcome. The S7-200 stores data (setpoints from the touchscreen) in RAM. The RAM is retained by capacitors that last (according to Siemens) for 2 days if the CPU has no power. In reality you will find your data lasts longer than that, but you should use the 2-day backup for your project planning. The S7-200 has an EEPROM that stores data and program logic. Upon a power failure when the capacitor or battery backup power fails and causes the setpoints in RAM to be lost, the default values from the EEPROM are used. You can see how it would be valuable to have "safe" setpoints in the EEPROM in the event this occurs. See my comment below about how to do this. ================================================= Option #1: On projects in which there are many setpoints we budget the extra money for a battery cartridge. In the event there are safety issues regarding battery failure, the option to write safe values to cpu eeprom is the responsibility of the programmer. See my comment below about how to do this. Option #2: On projects in which there are not very many setpoints and/or money is an issue we use plc code to detect when a setpoint changes and we write the setpoint to the CPU EEPROM upon change. In this way the setpoint is retained regardless of capacitor (or battery) backup. Good programming habit that is the catch-all regardless of the above options: When you are finished with your program and have debugged the machine, write the data to EEPROM. This is done by placing the CPU in stop mode and using the option in the MicroWIN software under Debug. The way it works is the software first sucks all of the data out of the cpu ram to your computer, then writes it back to the cpu's eeprom. Then you are prompted if you want to save that as your offline data block. I always do save it so I have a copy. I hope this helps explain how this process works. If you need examples of the ladder-logic code used to detect a change in a setpoint and write this to the cpu's eeprom, let me know. I can post or email you an example program. Caveat: Again, this information is based solely on my experiences with the S7-200. Your comments / suggestions / corrections are welcome.
	"I never let a cowboy make the coffee." Yeah, thats what Granny always said to my Grandad. And he'd say: "Never tell a joke that ain't that funny more than once." "And if you wanna hear God laugh, tell Him your plans." Van Zant "Help Somebody"
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4/1/2006 2:34 AM	Rate (0)
Berg Silver Member Joined: 1/17/2006 Last visit: 11/18/2024 Posts: 554 Rating: (29)	Hi Mojo, I've read your answer and please, I'd like to see an example about it. Could you put the file example here on forum ??? Thank you ... Regards, Berg
	"Educate the children and it won't be necessary to punish the men." Pythagoras
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4/1/2006 10:09 PM	Rate (0)
Mojo Bronze Member Joined: 3/27/2006 Last visit: 10/11/2024 Posts: 90 Rating: (13)	Sure. Here is a simple "brute-force" method of detecting a change in an integer setpoint such as would be used for a timer setpoint. Only one rung of logic is used for each setpoint. The example program contains ladder-logic code for five setpoints, VW0 - VW8. You can read the help for the SMB31 to learn how to set up the eeprom write for other types of data (byte or double-word). It is all about whether you set or reset the first two bits insmb31. To test the code you could load the program and then change the setpoints. Next, download a blank data block to the PLC. Third, go online and change the setpoints. Fourth, upload the online data block. After savingthe online data block to your PG/PC, examine it offline. You should find the setpoint values, indicating the logic wrote to the EEPROM. (The data will belisted in bytes in hex format, not easy to see at first.) EDIT: Forgot to say this program was created in MicroWIN version 4 + SP2. Attachment EEPROM.zip (764 Downloads)
	Last edited by: Mojo at: 4/1/2006 10:12 PM "I never let a cowboy make the coffee." Yeah, thats what Granny always said to my Grandad. And he'd say: "Never tell a joke that ain't that funny more than once." "And if you wanna hear God laugh, tell Him your plans." Van Zant "Help Somebody"
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