Simple SD card support

M

MFB

Senior Member
The project described in the following link started me thinking how useful it would be if the PICAXE supported commands to interface with SD cards via the SPI port. There has recently been a lot of discussion on the forum about how to use dedicated SD card interface modules and most of the complexity seems to be associated with the type of powerful random access features offered by FAT16 etc.

However, there must be lots of data logging applications that don’t need random access, where using the SD card like some form of big eeprom (or cassette tape!) would be quite acceptable. The PICAXE would be even more useful if this type of simple SD support was embedded.

www.captain.at/electronics/pic-mmc/
 
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demonicpicaxeguy

Senior Member
since i've given up on the sd cards due to many many reasons ,(see previous posts/rants )

i've gone to xd cards as the interface is simpler, they are quicker to write to,the only downside is a lot of pins to hook up,

i'm currently doing an i2c based xd card interface module based on a pic16fxxx running at 20mhz which in it's current config requires only 5 pins (5v,gnd,scl,sda,ready) (the sd cards need 7 ) also the added bonus of simple setup via a 3 pin interface with the aid of a terminal program (eg hyerterminal)
 
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Dippy

Moderator
We spent a lot of time doing an SD interface for PICAXE.
To 'embed' the code would take up a lot of space if you want FAT control.
In fact it occupies a helluva lot of space in a 18F2520 if u want error checking and fool-proofness and card-protection/detection.

One of the reasons we chose SD was the commonness of SD interfaces in PCs. XDs usually need an add-on adaptor. No big deal but is another box to lose (not loose). I'm not criticizing.
 
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M

MFB

Senior Member
New commands for X2?

Dippy,
I quite agree that implementing a full PC compatible filing system like FAT/16/32 would demand a lot of resources. That’s why I was interested in the possibility of a simpler non-random access SD card interface. Which could offer a useful alternative for those ‘sequential’ logging applications, where the card did not have to be read directly by a PC.
 
hippy

hippy

Ex-Staff (retired)
@ MFB : I think a major problem is that even an extremely simple MMC/SD interface is actually quite complicated, and the way MMC/SD works requires quite a large RAM buffer to use them effectively.

That said, it would be nice to be able to use MMC/SD just as if it were I2C Eeprom. The $64,000 question is whether Rev-Ed feels there is enough need or justification to invest the time and effort into developing the required firmware.
 
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