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 Posted: Jun 22, 2004 - 09:41 PM |
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Joined: Jun 22, 2004
Posts: 1
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Hi,
New to AVR Freaks!
Have a question accessing the EEPROM using Codevision. We are using the EEPROM to store nonvolatile cal/config data for an application. Looks like Codevision wraps up the EEPROM read and writes in their library so all you have to do is declare a variable as eeprom (ex. eeprom int Cal_Value;) and that stores that variable in EEPROM automatically storing a value in EEPROM when you assign it to that variable.
My question is if this is the case when I compile why does Codevision give me a warning that the eeprom variable in uninitialized?? That's the whole point, I don't want it initialized when I start up. I want to be able to use the last value stored in eeprom for this variable before that last power down. Or does initializing an eeprom declared variable only assign a default value that is only stored during the initial chip programming??
Am I missing something? Should I not use the Codevision eeprom declaration and store necessary data in the eeprom manually as described in the AVR ATMega16 user's guide?? 
Thanks in advance!! |
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Posted: Jun 22, 2004 - 09:51 PM |
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Joined: Feb 19, 2001
Posts: 25921
Location: Wisconsin USA
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prflory wrote:
... Looks like Codevision wraps up the EEPROM read and writes in their library so all you have to do is declare a variable as eeprom (ex. eeprom int Cal_Value;) and that stores that variable in EEPROM automatically storing a value in EEPROM when you assign it to that variable. ...
Yes, it is pretty transparent except for a couple of caveats like passing pointers (they must be of the type that the called routine expects).
Quote:
My question is if this is the case when I compile why does Codevision give me a warning that the eeprom variable in uninitialized?? That's the whole point, I don't want it initialized when I start up.
I understand your point. An SRAM global variable will indeed be given its intial value at each startup.
A CodeVision EEPROM variable, however, is >>not<< re-initialized every time that your AVR starts up. Rather, the initial values are used to produce the .EEP file at compile time. Then your programming system will/could program the EEPROM when the FLASH is re-programmed.
There are some here that never produce the EEPROM file, choosing to check the uninitialized EEPROM for the erased 0xff value for each byte and then do an initial configuration.
I do it the other way: I give all my EEPROM variables an initial value for a default configuration for a newly programmed system.
Feel secure that the EEPROM won't be re-initialized every startup. I've had all kinds of things in EEPROM on apps where flash became tight--menu strings, conversion factors, pointers to menu strings, etc.
Try a small trivial app with a few global SRAM & EEPROM variables with initializers, and then examine the startup flow in the resulting .LST file. [Remember that if you use AVRStudio to step through the app (a VERY useful exercise), that when you get ready to "Go" you must pre-load your simulator EEPROM values if you use the initializers. In 3.5x it is on the File menu under Up/Download Memories, IIRC.]
Lee |
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Posted: Aug 26, 2010 - 09:46 AM |
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Joined: Aug 26, 2010
Posts: 15
Location: Egypt
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Hello,
I have a project and I want to store in eeprom of my AVR
without putting an initial value in declaration of variables,
I use codevision software,can you help me??
I am waiting....
thanks for this website. |
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Posted: Aug 26, 2010 - 10:06 AM |
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Joined: Feb 12, 2005
Posts: 16323
Location: Wormshill, England
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Code:
int eeprom variable; // declare a variable in eeprom
...
int some_function()
{
...
variable = 1234; // give the variable a value.
...
}
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Posted: Aug 29, 2010 - 02:28 AM |
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Joined: Aug 26, 2010
Posts: 15
Location: Egypt
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Posted: Sep 01, 2010 - 12:23 PM |
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Joined: Aug 26, 2010
Posts: 15
Location: Egypt
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Hello!
I am working with ATMEGA 8535 Ic ,I use codevision ,and a 4*3 keypad for numbers ONLY.
I need a method,that I can use to print strings and characters on the LCD from keypad.
Is that right that I use that keypad ,or I must build a special keypad??
and if I used a special keypad what is the C code shall I use??
thanks in advance. |
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