I want to implement a removeable media in my next project. I have read some of the interfacing specs for compact flash (CF) and Secure Digital (SD).

The SD uses an SPI interface with 9 pins and the CF uses a 36 pin interface.

Has anyone already completed such a project with any type of removeable flash media?

Daryl

No, but I've looked into it a little for my own future use. I haven't seen the spec.s on CF, but I counted the holes in the connector on the CF module my bro-in-law has on his digital camera, and they totaled about 50. It could be they're not all hooked up, but still, 36 is an awful lot, especially when it's 3.3V or less and you probably want to interface to 5V. You'll have to have an awful lot of bidirectional voltage converters-- not practical at all.

SD and MMC (MultiMediaCard) use the same case and connector, but MMC is an open standard and you can get the spec.s to work with without spending a fortune for the license and signing non-disclosure papers and all you have to go through on SD. A recent article in a trade magazine I get predicted that for this reason, MMC will be overtaking SD in popularity and becoming more dominant.

The SPI mode on MMC's also requires a 3V interface; but besides power and ground, you only need 4 signal lines, and they're all monodirectional, making it really easy to connect and use an LM339 for level translation. There's data-in, data-out, clock, and select.

If size is an issue, consider that MMC is half the size of CF and will take a lot less room for interface circuitry. I haven't looked at Fry's in a couple of months for MMC flash memory densities, but 1GB was supposed to be available by the end of this year.

This one I can help with!

A compact flash STORAGE card (IO cards such as wifi and stuff are slightly different), are just IDE disk drives.

You can get an adapter with ZERO electronics that lets you put a compact flash card in your desktop machine as an IDE disk drive.

So, since IDE is a 5 volt system, all CF cards are gauranteed to take at least 5 volt levels.

Many of them can also take 3.3v, so if you're using 3.3v chips, you're in luck there too. It is simply a choice of the designer. The hard work is done in the little card.

As a caveat, when the card is in 'IDE Mode', it is officially NOT hot-swappable. So, you probably want to read the spec and get it into 'Memory Card Mode', which isn't hard. But it still runs at 5v. 'IDE mode' vs 'Memory Mode' is a layer 2 issue, not a layer 1.

Yes, I'm a network software engineer.

You might get some ideas from this:

http://www.circuitcellar.com/echips-pdf ... 1mspdf.pdf

Thanks for the link. Thats a good start. I downloaded the CF spec yesterday. This might be an option. I'd like to build a subsystem that takes care of the actual File I/O and responds to a few commands (open, close, del, dir, etc.) One goal would be to make the file structure compatible with MS DOS so the media could be swapped between PC and host 6502 system. That may be too much though.

Anyone know where I can get a copy of the DOS specification?

Daryl

A CF hard drive for the Apple II can be found at:

http://dreher.net/?s=projects/CFforAppl ... I/main.php

--
Paul

Paul,

That's a great link! Thanks!!!!

Daryl

Modifying that Jameco board for the Apple is a great idea. I'm thinking about getting a few of those myself. I remember seeing boards specifically intended for the Apple many years ago in the Mouser catalog. If memory serves, those boards struck me as pricey at the time, but they might have had traces in a "solderless breadboard" style layout (I don't really remember). Still, I kind of wish I had gotten a couple. I'd love to be able to find something like that where I didn't have to modify the board.

It seems to me that the Apple would make a good system for experimenting with 6502 hardware ideas, since you've got memory, video, software tools, etc. already there. Plus, even if you make a serious mistake and damage something, an Apple can be replaced relatively easily and cheaply these days. Of course, for some things you'd be better off just building your own SBC, but the Apple hardware was pretty flexible.

http://www.freedos.org/
That might be a good place to look.

Thanks! I'll give it a look.

Daryl