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Confusion regarding MMC pins and MMC driver...

 
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arunb



Joined: 08 Sep 2003
Posts: 492
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Confusion regarding MMC pins and MMC driver...
PostPosted: Sat Sep 08, 2007 2:13 am     Reply with quote

Hi,

I am using the MMC driver in the CCS folder to read and write to a MMC card.

However I need help in identifying the pins.

According to the MMC specification version 3.1 the 7 pins of the card are named as

Pin 1 RSV NC
Pin 2 CMD I/O/PP/OD Command/Response
Pin 3 VSS1 S Supply voltage ground
Pin 4 VDD S Supply voltage
Pin 5 CLK I Clock
Pin 6 VSS2 S Supply voltage ground
Pin 7 DAT

In the MMC driver code the pins are named as

#define MMC_CLK PIN_B1
#define MMC_DI PIN_B0
#define MMC_DO PIN_B3
#define MMC_CS PIN_B2

The supply, ground and the clock pins are clear enough, but where should the pins CMD and DAT be connected....???

thanks
arunb
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Sep 09, 2007 3:16 pm     Reply with quote

Download the Sandisk MMC manual:
http://www.sandisk.com/Assets/File/OEM/Manuals/manual-rs-mmcv1.0.pdf
Look at Table 5-1 on page 69 in the Acrobat reader.
It shows the signal names for MMC mode and for SPI mode.
Now you can clearly see how to connect the pins.
Code:

PIC MMC_CLK PIN_B1  to SCLK on MMC card (pin 5)
PIC MMC_DI PIN_B0   to DO on MMC card (pin 7)
PIC MMC_DO PIN_B3   to DI on MMC card (pin 2)
PIC MMC_CS PIN_B2   to CS on MMC card (pin 1)

Also, the signal levels are important. THe MMC card is intended for 3.3v
operation. It's easier if you run the PIC at +3.3v. If you run the PIC
at +5v, then you need to put in some level converters. Be very careful
about this. There are articles in the forum archives on this topic.
Search the archives for the keyword: MMC

Also note the requirement for pull-up resistors on two pins, per ckielstra:
http://www.ccsinfo.com/forum/viewtopic.php?t=28732&start=14
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