# EEPROM

### What is EEPROM?

EEPROM (Electrically Ereasable Programmable Read Only Memory) is fast read/write memory that doesnt clear on power-down. It can be used to store data like bite point, preset number, LED brightness settings, etc. When you power up the controller, the settings will be what you left them on power down. It will also allow you to adjust your presets with your controller, instead of hardcoding it in the firmware. 

With EEPROM hooked up, DDC will remember which preset you last selected, and the following settings for all your presets:

* Bite point
* LED brightness
* Throttle hold value
* Brake magic value
* DDS switch position

This will override any global values set in your [presets. ](https://dahl-design.gitbook.io/ddc/3.-coding/advanced/presets/32_presets.ino)But adding fixed per-preset values in the firmware will again overwrite EEPROM. 

Having EEPROM also allows you to use clutch functions with automatic calibration. 

### Does my board have EEPROM?

* The **Atmel 32U4** (board such as Pro Micro, Leonardo, etc) natively has 1024 bytes of EEPROM available, which has built-in support from DDC. You just have to turn it on. 
* The RP2040 can use some of its flash memory as a replacement for EEPROM, set to 1024 bytes. You have to turn on this feature. 
* The **Dahl Design CB1** has 65 536 bytes of EEPROM available, and EEPROM is automatically activated. 

All other supported boards ***does not*** have EEPROM.

Using flash memory as EEPROM works fine for a DIY project, but this is not idea for a commercial product or any project with a custom PCB and you cant easily replace the controller board. It can't handle as many rewrites as a proper EEPROM IC (100-fold difference). For this reason, DDC also supports dedicated EEPROM chips:

### CAT24C512

DDC supports adding EEPROM in the shape of a I2C device called CAT24C512. Since it runs on I2C protocol, it will need to use the SCL and SDA pin on your microcontroller. More on this in the [wiring ](https://dahl-design.gitbook.io/ddc/2.-wiring/eeprom)section.

<figure><img src="https://1937097571-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FXsx2Pyx5QBO3iWZFpmmR%2Fuploads%2FUEzDvmtSq9ANKXLlL5cz%2Fimage.png?alt=media&#x26;token=5d2676be-5039-4fd9-88fe-e9515677b122" alt=""><figcaption></figcaption></figure>


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