Micro SD card interfacing to pic18f67k22

[manisha]

Haiiiiii

I am using development board of micro sd card which is from embeededmarket.com. I have connected to 5volts line i.e cs,di,do and sck pins. and set sdi pin of microcontroller as input in tris configuration and others as output and used ex_mmcsd.c example and I am able to read and write the data from particular location even if the SD card is inserted or not. THen tried with FAT16 driver and ex_fat.c file and in this, when entered the commands like mkdir,format etc. I am getting errors in response.. Not understanding where the fault is?

Can anyone please tell me how exactly micro sd interfacing code is done???

And one more is does Micro SD card support SPI mode since in some places it is given as optional...

Expecting a quick response.......

[Ttelmah]

5volts?........

SD, and MicroSD, use 3.3v, not 5v.
5v anywhere near them is asking to kill the card.

The CS line, and the SCK line (and preferably the SDI line to the micro), must have pullup resistors to 3.3v. 10K is recommended for CS, and 50K for the other lines. Some sources simply recommend 10K on all four lines.

Card must be MicroSD, not MicroSDHC. The libraries do not support HC cards.

If you are using the examples, you don't need to set TRIS. With CCS, for 99% of code, do not touch the TRIS registers, the compiler handles this for you.

Best Wishes

[asmallri]

[manisha]

Thanks a lot for your replies......

I am sure that the voltage at the card is 3.3 volts logic even if microcontroller has 5 volts logic since 3.3 volts regulator is in between and also all the IOs (CS,DI,DO,SCK) near memory card are now at 3.3 volts logic. So no chance to kill the card.

And I think the problem lies in the capacity of card i.e I am using 4GB kingston i.e SDHC as specified on the memory card. And I think the drivers provided in the library are not supporting that card.

Can anyone please suggest what drivers I should use to program 4GB microSDHC card???

[Ttelmah]

Even if the card was SD, you would have problems.
How are you adapting between 3v and 5v on the data lines?. Key point to understand, is that the 3.3v output of the SDO line on the card, does _not_ go high enough to be seen by the PIC running at 5v, as a logic 'high', if you are going into an input that uses Schmitt buffers. These _require_ the signal to go up to typically 0.8* the PIC's supply rail (0.7* in some cases). 3.5 to 4v. The SDO line then can never actually be 'seen' by the PIC. Hence you need to have a proper 3.3v to 5v buffer on this line, or it'll never work.
Hardware SPI uses Schmitt inputs.
The other lines _can_ be adapted by just using resistive dividers (but this can be unreliable at higher data rates), but the SDO line can't....
You can feed this line straight into the PIC, _only_ if you use software SPI, and select pins on your PIC that have TTL input buffers (2.4v high).

Interfacing properly between the levels _requires_ proper level shifting IC's in both directions (or much easier, switch to using a 3.3v PIC).

The fat libraries actually work OK with the larger cards. The bit that doesn't is the MMC interface code. The larger cards change to using block addressing, rather than byte addressing, using a fixed 512byte block. There are commercial libraries that'll handle this, or it is fairly easy to modify the existing driver. However you need to get your hardware working first. I'm sure your's isn't.
Look at brushelectronics for a full driver, and look at the circuits they publish for 'how to connect'.

Best Wishes

[manisha]

[ckielstra]

[manisha]

The compiler version which I am using is Version 4.120

[manisha]