Byte storage on eeprom?

TCP71

Forgive my ignorance if this has been covered a million times.

I am trying to store a byte or long of data on the eeprom that has my propeller code (24c512 eeprom) for use as a status when the processor is shut down. Basically, I want to be able to access this data to know the status of the unit I'm controlling when it was last shut off and restore it to that mode on boot. Is there a simple way to designate a specific section of eeprom to store this, then I can load it when it boots up and make things the way they were?

Thanks for any help.

davidsaunders

It would be relatively simple to just store a value at a given address. The bigger question is, how often do you plan on updating the value? There are a limited number of available write cycles in the EEPROM.

TCP71

Only when the status of the unit is changed by the user. Not very often. less than 200 time/year. Basically just to "remember" that the unit was running in mode A when it was turned off at night and starts out again in the morning in mode A. 8 bits should cover all the possible variations I need, I just need them to be checked when the unit starts up.

Thanks.

Dave Hein

You can use Mike Green's Basic_I2C_Driver object to update a value in in EEPROM. Just use the following code:

obj
  i2c : "Basic_I2C_Driver"

dat
  status byte 123 ' Initial value

pub main
  i2c.Initialize(28)
  ...

pub UpdateStatus
  i2c.WriteByte(28, $A0, @status, status)
  repeat while i2c.WriteWait(28, $A0, @status)

TCP71

Thanks, that's quite simple. Is there any way to "lock out" a byte of the eeprom from having it being used during the compiling of code so it is always available and never impacted by the propeller code itself?

Rayman

I think the easiest way to do this is with Andy Lindsay's PE Kit Lab App:

http://forums.parallaxinc.com/forums/default.aspx?f=25&m=219237

Mike Green

The entire 2nd 32K area in a 64K byte EEPROM is completely untouched by the Propeller Tool. If you only have a 32K byte EEPROM, you can use the end of the EEPROM for storage. It would be very unusual for a Propeller program to use every last byte of the EEPROM and the end ($7FFF and down) is the last to be used. You would lose the stored value when you download a new program to the EEPROM since the ROM bootloader clears the EEPROM to zero when it copies the program from RAM to EEPROM, but you can design your program to handle that case.

TCP71

Thank you. so I could use any of the 32k in the high address range of the 64k chip. Unless I actually program new code into the eeprom, my information will remain intact? Accessible via the I2C driver shown above?
That would be perfect.

Dave Hein

Yes, you could use any location in the high 32k part of the EEPROM. The prop tool doesn't touch this part of the EEPROM when you reload a program, so your data will remain there. You just need to read the data at the beginning of your program as shown below.

Dave

con
  StatusAddress = $8000

obj
  i2c : "Basic_I2C_Driver"

var
  byte status

pub main
  i2c.Initialize(28)
  status := i2c.ReadByte(28, $A0, StatusAddress)
  ...

pub UpdateStatus
  i2c.WriteByte(28, $A0, StatusAddress, status)
  repeat while i2c.WriteWait(28, $A0, StatusAddress)

TCP71

Thanks!! I will run with this.