PIC look-up tables vs. EEPROM

[Hank Fletcher]

When you use a look-up table with a PIC, where does the data get stored? For instance, the 18F4685 has 48K of program memory, but only 1k of EEPROM memory, so depending on where those look-up tables are stored, I guess that would effect considerably how much data you could store in a look-up table, just on the PIC.

I guess I had always been thinking on the presumption that look-up tables fell under the category of program memory usage, but maybe I'm wrong about that?

 

[Nigel Goodwin]

When you use a look-up table with a PIC, where does the data get stored? For instance, the 18F4685 has 48K of program memory, but only 1k of EEPROM memory, so depending on where those look-up tables are stored, I guess that would effect considerably how much data you could store in a look-up table, just on the PIC.

I guess I had always been thinking on the presumption that look-up tables fell under the category of program memory usage, but maybe I'm wrong about that?

Lookup tables are stored in program memory, not the EEPROM - EEPROM data memory is an entirely different thing, although you could use it to store tables if you wanted, but it's rather slow.

 

[Hank Fletcher]

Good to know, thanks!

Can you give an example of an application where it would make more sense to store data in the EEPROM memory as oppose to in program memory?

 

[Nigel Goodwin]

Good to know, thanks!

Can you give an example of an application where it would make more sense to store data in the EEPROM memory as oppose to in program memory?

The only thing that comes to mind is data that needs to change occasionally, a good example would be the entry code for a digital door system - the code could be stored in the data EEPROM as a table, and altered from the keypad as required.

Notice my keypad lock tutorial simply stores the code in program memory, but I do mention EEPROM as an obvious modification.

 

[Mike - K8LH]

Good to know, thanks!

Can you give an example of an application where it would make more sense to store data in the EEPROM memory as oppose to in program memory?

Store strings for an LCD for example and other 'constant' data which never changes in program memory. Store data that may need to be changed, such as product configuration data, baud rate, time zone, etc., in EEPROM.

Mike

 

[ericgibbs]

Store strings for an LCD for example and other 'constant' data which never changes in program memory. Store data that may need to be changed, such as product configuration data, baud rate, time zone, etc., in EEPROM.

Mike

hi,
Useful for storing 'calibration' data.

 

[bryan]

Data logs etc so they persist after power from the PIC is removed.

 

[atferrari]

All what is a user selection.

All user choices like pre-tuned stations in a car radio, are stored in eeprom.

The same for cofee makers, printers and almost any device that has to keep a set of user's (selected) options for the next time it is turned on.

 

[CCD]

Look-up tables are usually meant for a fixed application, like generating sine-wave of a fixed frequency, hence, they are always stored in the Program/Code Memory.
EEPROM is for different use altogether, as mentioned, for password storage, user setting storage etc, which may change later.
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