SD / MMC memory extension for Microcontrollers

To add storage space to microcontrollers is very easy with Secure Digital cards. SD Card Association site has a Physical layer specification document that describes the card very briefly. It does not explain the full protocol specification though.

Why use SD Card? Using SD cards with microcontrollers has a few advantages. First of all it is very cheap. You can find very good deals on 64MB cards. I bought mine for less than $2. Secondly the access protocol is very similar to a 3 wire bus / SPI.

Here are some examples of interfacing the SD cards to various popular microcontrollers.