Hi Guys,

You don't need to go to the trouble if interfacing as a USB master to read
CF cards.. You can interface a PIC to them directly reasonably simply. I've
done this for a MP3 player for a client of mine. The CF card has a (slower)
8-Bit interface as do Hard drives.. But speed shouldn't be too much of a
problem. To make it faster you would have to use a PLD to implement a
"proper" IDE like interface.

3M and many others make CF card connectors, I'm sure you should be able to
get them from digikey.

You can also interface a PIC to a IDE hard drive (web pages out there on
doing this).. I used a '877 for my MP3 player..

Shouldn't be too hard to design a storage unit.. I don't think you would
need any extra RAM for buffering as HDs and CFs generally both use 512 byte
blocks so you read the block out of the CF and straight into the HD..

I haven't looked to hard at it but I'm sure you could do a minimal
implementation with very little extra glue logic.

Just looking at the schematic for my MP3 player, ok for the CF card, you
need an 8bit data bus, 3 address lines, Output Enable (Read), Write Enable
(Write), Card Detect, Reset (optional), Ready/Busy (optional, but
recommended).

That's 16 connections. You would also want a Chip Enable if your sharing
with a IDE HD.. Say 17. Then to interface to a HD (from memory here.. could
be wrong) you have basically the same connections and almost the same
registers that you talk to. You would need a different chip enable for the
IDE disk.. I'm sure you could get away with around 20 pins at most. A '877
would then still have enough pins for a LCD and some buttons if you were
tricky about the connections..

Reading and writing the raw data blocks (LBA mode) is pretty simple.. you
set up some values in certain registers using the address pins to select the
register and data and the OE and WE pins to read and write. Basically you
query the registers to get disk format information (num sectors, size etc..)
then you setup an address register and start reading or writing to a
different register to stream the block of data in or out..

Once you can read and write the basic blocks, you need to implement some
file system decoding.. this can get a little tricker because there are
several different FAT file systems to accommodate, but not to hard..

Trouble is that a Hard Drive is going to eat batteries.. probably best to
make it externally powered by a plug pack or car cigarette lighter socket..
Have the PIC spin up the HD when it detects a CF card inserted, it then
works out the file system on the CF card and HD, displays some details on
the LCD and waits for the "copy" button to be pressed to begin copy or the
"erase" button to be pressed to erase the CF card perhaps..

I'd have it create a directory on the HD for each "date" (would need a Real
time clock chip to help with this) then each CF card of pics entered on that
day would get its own sub directory and you copy all the files into there.
Then erase them on the CF card. You want to have at least 2 levels of
directories because some FAT file systems have limited number of entires per
directory and you could conceivably run out of directory entires.

Cheers,
Ash.

---
Ashley Roll
Digital Nemesis Pty Ltd
www.digitalnemesis.com
Mobile: +61 (0)417 705 718




> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Brent Brown
> Sent: Saturday, 15 June 2002 12:24 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [OT]: digital camera picture storage
>

> Back to project ideas though: USB card readers for PC's are cheap and
> work well. That gives you a good connector for the card. Then you
> need a USB master controler. Not many ideas there sorry. IDE
> interfaces for micro's have been done before though.
>
> Another idea I can visualize is a 3.5" floppy drive sitting on top of
> a 3.5" hard drive. Buy a memory card floppy drive adaptor and bang,
> all your hardware is done for you. With this scheme the floppy drive
> and hard drive interfaces are very similar and may be able to share
> circuitry and software in your micro interface. Just detect the
> floppy inserted and dump all contents into a new folder on the hard
> drive and turn an LED on to say it's done. Maybe put the hard drive
> in a removable bay to make it easy to get the data back into your PC.
>
> Sounds easy, but I know there will be a heap of work involved.
> Probably more software than anything else.

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