SD card & ATmega16

gregor001 · Joined: 01 Mar 2007 Posts: 5

hi:)

does anyone have a working example for
-Bascom AVR/8051
-ATmega 16 or some in this price range (atmega128 is cca.16eur in our country-expensive for me)

.. to write and read something on SD card

IMPORTANT: without BASCOM-DOS commands, only AVR or 8051

is it possible?

thnx
Gregor

thiagorod · Joined: 13 Nov 2008 Posts: 109

I think you should take a look at

http://www.dosonchip.com/

I am gonna use this chip on my next project. You send UART commands to the chip and it handles all the FAT32 read/write on SD cards.

Thiago

kubic · Joined: 03 Nov 2008 Posts: 42

try google for : Phils FAT Library for ATA & MMC/SC Cards (BASCOM)

AdrianJ · Joined: 16 Jan 2006 Posts: 2483 Location: Queensland

You can read and write to the card using Bascom commands DriveReadSector and DriveWriteSector in 512 byte chunks, without AVR-DOS. Since you dont need the file buffers that AVR-DOS uses, it should work fine with an AtMega16, as long as you have 512 bytes of RAM spare. But you cannot read the result with a PC, at least not with the standard FAT filesystem.

I would query your pricing though, we buy Atmega64 for essentially the same price as Atmega16 here in Aus, about AU$6, would be around 3 euro.

I saw the dosonship bare chips on Sparkfun for US$12.95

thiagorod · Joined: 13 Nov 2008 Posts: 109

It is mandatory on my project to write data on FAT32, to be read under Windows. I didn´t know this solution from Phils, sounds nice. Although I couldn´t find hardware schematics on how to connect the SD to AVR and didn´t find good examples writing/reading SD.... I am using ATMega8515.

AdrianJ · Joined: 16 Jan 2006 Posts: 2483 Location: Queensland

I dont know that library, but I doubt it takes any less RAM than the AVR-DOS of Franz Vogel. At the very least, you need a buffer of 512 bytes, because that is what a card sector is. You can use one buffer for both data and directory, but it costs you a lot of swapping and hence speed. As well you need some global variables for the filesystem, plus the FAT table.

If you run the processor at 3.3 volts - same supply as the card, you just direct connect the hardware SPI lines to the card, else you should use a voltage conversion buffer - lots of info on the AVR-DOS forum about the connections needed.

(edit)
I just had a very quick look at that library, and it uses at least two 512 byte buffers, plus the usual collection of global variables, so you need at least 1 Kb + of space, the same as the AVR-DOS library.

Processors are cheap, use an AtMega64.

thiagorod · Joined: 13 Nov 2008 Posts: 109

So you recommend to go with DOSonChip anyway? All the processing is off-loaded from AVR.

AdrianJ · Joined: 16 Jan 2006 Posts: 2483 Location: Queensland

No, I would recommend you use an AtMega64. Why add another unknown and special expensive chip when you can do it all with well tried and proven parts and software.

thiagorod · Joined: 13 Nov 2008 Posts: 109

Actually I use a platform based on ATMega8515. Doesn´t it have enough horsepower to run AVR-DOS ? I just need to write a few bytes of code in text-format file on a SD card.

AdrianJ · Joined: 16 Jan 2006 Posts: 2483 Location: Queensland

Unless your platform also contains some external SRAM, you are out of luck.

There are some work-arounds which would allow you to do this, they involve preparing SD cards with a file from a PC, locating the actual hardware sector the file is at, and writing to that address using the Bascom SectorWrite command. It is possible, but I would not say its easy.

Can we take this discussion over to the AVR-DOS forum ? There are more people over there who know about this stuff.

bzijlstra · Posted: Tue Dec 16, 2008 9:35 am Post subject: Vinculum VDIP-1 module

My two cents:

Have you considered using the Vinculum VDIP-1 module. You can connect a standard USB memory stick to your microcontroller and read and write it with RS232-commands.

Check http://benshobbycorner.nl

There was an article about it in november issue of Elektor.

Have fun
Ben Zijlstra

ex4 · Joined: 13 Jan 2006 Posts: 1062 Location: indonesia

hello Mr Ben,
always nice to have you posted your work here Very Happy

by the way,where is the tutorial that you usually write?been visiting your website
http://benshobbycorner.nl/
but got none there Shocked

also trying to open your website at
http://members.home.nl/bzijlstra
but cannot open it? Mad