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PIC A COMPACTFLASH CARD

by Mark Samuels

Start ý A Choice PIC ý Getting Connected ý Address Decoding ý The Identify Drive Command ý Laying the Foundation ý No Limits ý Sources and PDF

I am a gadget junkie. Anytime a new tech toy hits the market, Iým the first in line to buy one. However, when I bought a digital camera two years ago, it was not the camera itself that held my fascination, it was the cool little matchbook-sized card that stored all the pictures (see Photo 1). As more products appeared that used a CompactFlash card for removable storage, I was both delighted and despondent. Delighted because this seemed to end the apparent curse that my enthusiasm for a new format indicated its obsolescence (i.e., MiniDisc, CDi, etc.). And, despondent because every device that used a CF card seemed to have some serious processing horsepower, making it appear that using such an interface in lower-end designs would be difficult. When I discovered the Microchip PIC microcontroller, I knew it was my solution for integrating CompactFlash into my own projects. Now, I have the capability to add numerous megabytes of compact, removable, nonvolatile memory to virtually any system.

Photo 1ýCompactFlash cards are available from a variety of manufacturers in several different capacities.

The CompactFlash Association was established in 1995 to specify the format of what was to become a subset of the PCMCIA or PC card specification. The result is a removable media standard that uses fewer interface signals (50 instead of 68) and is roughly one-third the size of a PCMCIA memory card. The internals of the memory card consist of a smart controller, buffer, and varying amounts of nonvolatile memory. The specification also defines different modes of access to the card, including Common Memory mode and True IDE mode. While in True IDE mode, the card can be directly connected to an IDE bus with no active circuitry, which makes it a great way to add removable storage to an embedded PC. However, because I was planning to use an 8-bit microcontroller, I chose to access the CompactFlash card in its Common Memory mode, taking advantage of an 8-bit wide data bus in this mode, instead of the 16-bit data bus required for an IDE interface.

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