Post by thread:Re: [PIC]: EEPROM

Dear PicList Members Are there a limit to to read/write operations to a pic16f84... in other words, can I read/write to Eeprom say 4 times per second to "save" the status of my pic actions in case of a power failure so that the pic can left of where it stoped? Will the lifetime of the pic be reduced? For example if I have a action that was switched on at 10H00 and must switch of at 10H30. Say there are a power failure from 10H05 to 10H06. I want the pic - after reset - to switch the action back on if the stop time was not reached. If there was no flag saved in Eeprom that tells the pic to start the action again the action will be ignored untill the following start time. I ass-u-me that a write to Eeprom at the instant when the power fails can give unexpected results. How can one get around this? (without the use of a UPS or backup power) Regards lllllllllll \\ ~ ~ // ( @ @ ) o------oOOo-(_)-oOOo-----o | | | Francois Robbertze | | spam_OUTfr10TakeThisOuTmweb.co.za | | | o--------.oooO-Oooo.-------o -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

Hi Francois Without looking at the data sheets, I couldn't give you a precise figure, but there is a limit to the number of times that you can write to the EEPROM without errors and at 4 x per second, that would not take long. I'm sure you would be better off using a battery, back-up, and has the advantage of keeping a track of the time. Also a write to EEPROM has a time penalty, and may possibly use up a lot of your processing time, leaving little room for other things. Have a look through the components catalogues for suitable devices, and data sheets and application notes are fairly plentiful. Maybe some one else out there has a good design ? With best regards, Petra. {Original Message removed}

>> Are there a limit to to read/write operations to a pic16f84... in other words, can I read/write to Eeprom say 4 times per second to "save" the status of my pic actions in case of a power failure so that the pic can left of where it stoped? Will the lifetime of the pic be reduced? << Yes. The lifetime of the EEPROM is specified by the number of write cycles. For example, if the EEPROM is rated at 1,000,000 writes and you do 4 every second, then the EEPROM could fail in less then 3 days. If you need this kind of feature, you could try an external battery backed CMOS static RAM, or arrange for the PIC itself to be battery backed and asleep when the unit is "off". ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, olinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam.....mitvma.mit.edu

You can often reduce the number of writes dramatically be using some simple techniques: 1: spread the writes around. don't do all your writes to one location. this can require some tricky code to figure out what data is the newest. 2: don't write when you don't have to. if the value hasn't changed, don't write it again. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu

On Fri, 26 Jan 2001 08:29:21 -0500, you wrote: >>> >Are there a limit to to read/write operations to a pic16f84... in other >words, can I read/write to Eeprom say 4 times per second to "save" the >status of my pic actions in case of a power failure so that the pic can left >of where it stoped? Will the lifetime of the pic be reduced? ><< > >Yes. The lifetime of the EEPROM is specified by the number of write cycles. >For example, if the EEPROM is rated at 1,000,000 writes and you do 4 every >second, then the EEPROM could fail in less then 3 days. > >If you need this kind of feature, you could try an external battery backed >CMOS static RAM, or arrange for the PIC itself to be battery backed and >asleep when the unit is "off". ..or use a power-fail detect circuit to do a save-on-powerdown. You don't need a very big capacitor to run the PIC for long enough to ensure a safe eeprom write. -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

Dose anyone have C code for 24LC01B EEPROM? Gary-- _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Which compiler? CCS comes with a driver for it in the drivers directory... Dale -- "Curiosity is the very basis of education and if you tell me that curiosity killed the cat, I say only the cat died nobly." - Arnold Edinborough On Thu, 6 Dec 2001, Gary silva wrote: {Quote hidden}> Dose anyone have C code for 24LC01B EEPROM? > > Gary-- > > _________________________________________________________________ > Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body