Bad Eeprom write on '628???

[bethr]

Hi:
I am trying to save PORTB pin status on Power On Reset, then when power is restored the data will be the same there is my code:

start:
trisb=0
gosub update ' restore last portb value

mainlop:
portb = portb +1
gosub store_val 'update the value on rb to eeprom
pause 1000
goto mainlop


update:
read 0,last_val
PORTB= last_val
return

store_val:
last_val=portb
write 0,last_val
pause 10
return

is too simple, it means a loop where the portb is incremented once each second and then save the status on eeprom, but it doesn't work !
when I remove the power then I restore, th leds atached to the port b is a number different to the I can remember when the pic is shut off!

Ovbiously I init the eeprom data with a number before taht the pic can run on first time!
What I doing Wrong?
Thanks!

[Jerson]

You should not write to the EEPROM every second. The number of writes is limited if you know. Ideally, if you need to save, you should save only if there is a change in status of the port. This will reduce the number of writes.

This looks like a test program to me. So, please think of your real application. You may not need to update the EEPROM so frequently..

Jerson

[paul borgmeier]

1)You haven't declared last_val

2)If you lose power while writing to the EEPROM your saved value might be corrupt

3)You most likely will shut off power during the pause 1000 – in this case you would not expect to see the same number when you repower up. Say you had PORTB = 28 when the power went down (during the Pause 1000). 28 should be in the EEPROM. When you reapply power, the number 28 is read back and put on PORTB. a few microseconds later you add 1 to that and display the new value, which you see. Therefore 28 !=29.

4)Jerson is right – your eeprom is limited in the number of writes – how about detecting the power loss and writing the value to EEPROM before the power drops out?

5)

Ovbiously I init the eeprom data with a number before taht the pic can run on first time!

Not to me, I don't see it in your code.

[bethr]

Thanks by your comments friends, my real app is simple y try to make a ir (infrared) control box that control 4 relays the only that i need is save the last relays status when a possible reset ocurr!, it ensure that there is no change when the power suply is shut down!

last_val is a byte sized var, and I do not write a statemment as

" WRITE 0,1" ;INIT EEPROM

instead I mod the eeprom data memory in MPlab when i burn the Chips, so
How I can detect a power loss?, what is then the best way to do this type of things?
my idea is save the PORTB status ONLY when a new value is reloaded from a an Ir controller, instead each second as the above code is!.

Thanks Again!

[paul borgmeier]

>> How I can detect a power loss?

Lot of ways to do this ... without a schematic or more detail it is hard to say what is best. For moderately low power projects, I place a fast diode between the power supply and VDD. I also place a cap between VDD and GND. I then monitor the voltage from the anode of the diode (also connected to the PIC through a diode) and sense when it goes low (with ADC or Comparators). When it goes low, I shut off everything and write to EEPROM. I size the cap to give me enough time to do this.

Others might do this differently (like using BOD).

[bethr]

As you can see the schematic is very simple.
I try to make the changes what you say, view the ADDED.jpg file I think that this may work, today I also make code changes and i try again, let know if the the squematics looks like you say,

Thanks