Using EEPROM to store variables...

[Tom Gonser]

I would like to store some values in EEPROM, and then read these out later when I need them.. The problem is what I I2CWRITE is not what I see when I I2Cread... Where I THINK I store a '1', I see it read back as '127' or '80'...???

Consider this - I want to store a baud rate for SERIN2 - a value of "16572".

So, I create a varable:

WBD var Word ' variable to be stored
LOC_WBD = 20 ' memory location to store it

Then I write the value to EEPROM

Assume: WBD = 16572, then ->

I2CWrite DPIN, CPIN, CHIP1, LOC_WBD, WBD.byte0
pause 10
I2CWrite DPIN, CPIN, CHIP1, LOC_WBD+1, WBD.byte1
pause 10

-> I'd EXPECT I just stored the variable 16572 into memory location 20 and 21 (Word)

THEN to get it back, I'd :

I2Cread DPIN, CPIN, CHIP1, LOC_WBD, WBD.byte0
I2Cread DPIN, CPIN, CHIP1, LOC_WBD+1, WBD.byte1


WBD should be 16572... but it is not. What did I miss?

Same goes for BYTE sized storage of varables..

B0 = 1
LOC_B0 = 22

I2CWrite DPIN, CPIN, CHIP1, LOC_BO, B0
pause 10

( I think I stored '1' in memory location 22)

BUT:

I2Cread DPIN, CPIN, CHIP1, LOC_BO, B0
LCDout "BO is: ",#BO

Displays 127 or 80 - not '1'...


I am missing something FUNDAMENTAL here..

Tom

[mister_e]

will be interesting to know your EEPROM model before. Did you read/ compare your code+schematic to the PBP manual before? Have a search in this forum, you'll find a load of answer!!

[Melanie]

http://www.picbasic.co.uk/forum/showthread.php?t=587

You WILL need pull-up's on the Clock and Data lines (weak pull-up's just don't work reliably here)... 4K7 is recommended.

[Tom Gonser]

Deeper question - sorry - let me explain..

The external EEPROM is working.. I am storing and retrieving data. So yes, I know the lines are working, etc. I have pull-ups, etc.

However, I am trying to KEEP data alive even after power down, and this does not seem to be working 100%. Some survives, some does not!!

24LC512s - I am using two of them. The software can tell them apart, and know them as 'Chip1', and 'Chip2'. When I write data to the Chips, then retrieve it, I get valid data, even if I fill up both chips. It works fine at a gross level.

The issue is deeper than if the EEPROM is recording or not - it has to do with saving specific BYTES in EEPROM between power cycles..

My program writes logging data to the EEPROM in Page Mode. My data is 36 bytes long, so I actually read 3 times into an array of a size of 108 (which works on the 18F2525). That way each page has 108 of the 128 bytes used.

1. I ALSO want to store some variables that I need BETWEEN power cycles in EEPROM.
A. the last used memory location, so when I start up again I know where I ws.
B. the user selected 'baud rate' for download
C. the 'passthru flag' - tells the code if it should just record to memory only, or also send that data to the serial port.

SO - I write my LOGGING data in memory positions

128-64000 - in chip 1 -> saving address 0-127
0-64000 in chip 2

I WANT to use the first 'page' on chip one as a place to keep persistent variables. SO I write to the address range 0-127 for these variables.

The memory locations are defined as:

Symbol ADR_loc = 10 ' next usable address
Symbol CHP_loc = 12 ' the chip we are on
Symbol D_baud_loc = 14 ' the download baud value
Symbol pass_loc = 20 ' the flag for passthru
Symbol wpt_loc = 30 ' the flag for waypoints
Symbol W_baud_loc = 40 ' waypoint baud rate


Then, I collect data from the user or from the program, and I2CWRITE the data into the memory locations as per above. The PROBLEM seems to be that when I write for example a '1' into "pass_loc", when I I2CREAD that same memory location later DURING the same power cycle, it is fine - it reads back what I'd expect. The PROBLEM is that if I power cycle, the data gets smashed...

HOWEVER, the data I write in PAGE MODE appears to survive a power cycle....

Any ideas why?? Can you not save persistent data to EEPROM?

[NavMicroSystems]

. . .Can you not save persistent data to EEPROM?

of course you can, this is why we use EEPROMs!

I see several reasons for EEPROM data not being what you expect it to be:

It has not been written to EEPROM (is your timing ok?)
or
it is being overwritten during the power up.

In both cases there must be something wrong in your code.

I assume you have already tried a different chip to ensure the EEPROM itself is ok.

[Tom Gonser]

Have not checked memory - I will. Funny tho how perfectly well it works AS LONG AS I DON'T POWER DOWN.. So the culprit MUST be something in the intitialzation somehow?? hmm.

Maybe the fact I am declaring the memory locations as SYMBOLS is a problem? When I start up, for example, I declare the memory location to store baud rate as

wptbd Symbol = 10

Does this need to be a VARIABLE? I will never write the value for Waypoint Baud to anywhere EXCEPT position 10.. that is so I know where to get it when I need it.

I saw mention of not using SYMBOLS in I2C..

??

[mister_e]

O.k this is why,

with your EEPROM, your address must be a word sized variable, so use

wptbd VAR WORD
wptbd = 10

And with wptbd Symbol = 10 written as is you didn't get any compilation error??