[sdiy] dsPIC fun board

[Eric Brombaugh]

Ingo Debus wrote:
> 
> Am 16.01.2009 um 22:52 schrieb Eric Brombaugh:
> 
>> An I2C serial EEPROM would probably be pretty easy to add
> 
> Don't know much about the dsPIC, can't you write to the internal Flash 
> memory from within the user program? Almost every microprocessor I came 
> across in the last few years could do that.
> In this case an EEPROM is not needed for nonvolatile storage.

This is true. The only caveat is that the write endurance of the on-chip 
flash in the dsPIC is somewhat limited. MCHP only guaranteed about 1000 
cycles for the initial parts, although they may have upped since I last 
looked. That's plenty for development purposes, but for use as 
non-volatile storage in the end application it might be a bit shy of 
what's needed.

Inexpensive EEPROM on the other hand can be found with write endurance 
specifications in excess of 100,000 cycles. For instance, the 24AA256 
32k x 8 I2C EEPROM I'm currently considering guarantees > 1,000,000 
write cycles, takes up only a little board space and costs about $1.

EEPROM has an additional advantage in that its write timing is 
independent of the operation of the main processor. If you want to write 
data to the dsPIC's on-chip flash then the whole processor has to halt 
while erasing & writing the memory. With an off-chip EEPROM you send the 
data out via I2C and go about your business while the external part goes 
through the write cycle.

> Also, in my experience, EEPROMs are unreliable.

This interests me. What specifically were the pitfalls you experienced 
in using EEPROM?

Eric