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Interfacing to a Multimediacard (MMC)

 
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tberckmann
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Interfacing to a Multimediacard (MMC)
PostPosted: Tue May 24, 2005 11:11 am     Reply with quote
I am attempting to connect a PIC18f6720 to an Atmel AT45DCB008 MMC using the SPI bus.

I have confirmed that the card is receiving the required 3.3V, that it is properly grounded, and that the pins are properly connected to the bus.

I initialized the card with the following code:

Code:


SETUP_SPI(SPI_MASTER | SPI_CLK_DIV_4);

SSPSTAT |= 0x40;                          // set CKE - bit 6
SSPCON1 &= ~0x10;                         // unset CKP - bit 4

chip_select(NONE);                    // set SS = 1 (off)

for(i=0;i<10;i++)                       // send at least 74 clks on
{
        SPI_WRITE(0xFF);
}

chip_select(MMC_CS);                     // set SS = 0 (on)
delay_us(250);


SPI_WRITE(0x40);                        // send reset command
SPI_WRITE(0x00);                        // all the arguments are 0x00
SPI_WRITE(0x00);
SPI_WRITE(0x00);
SPI_WRITE(0x00);
SPI_WRITE(0x95);                        // precalculated checksum

SPI_READ(0xFF)


I confirmed (using an oscilloscope) that the write commands were in SPI mode 0 (that the command was available on the rising edge, and properly formatted, etc...) and that all of the timing was correct. However, in the final SPI_READ command, there is no response from the card, despite polling for several seconds.

Does anyone have some troubleshooting tips or suggestions for me?
ckielstra



Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands

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PostPosted: Tue May 24, 2005 11:32 am     Reply with quote
The AT45DCB008 has a physical connector and dimensions that are equal to an MMC card, the used protocol however is completely different. I had a quick look at the datasheets and the protocol looks much easier than the protocol for the MMC card.

For a detailed description of the AT45DCB008 you have to look at the datasheet for the AT45DB642
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