I've been trying for sometime to interface a Sandisk 16MB
MultiMediaCard with a Parallax Basic Stamp 2 without success.
The 5v Stamp pin signals have been converted to MMC levels (~3.18v)
and using various application documents that I've found,
I think I've got the physical construction right (logic probe looks
good) but it doesn't act exactly the way it should. Specifically:
To power up the card and initialize it into SPI mode (which I need to
use), the documentations says to
1)send at least 74 (80 is suggested) clock pulses
2)set CS pin to LOW
3)send the reset command (CMD0), which is 0x4000 0x0000 0x0095 (I'm
using SHIFTOUT/MSBFIRST)
4)send 8 clock pulse as delay
5)SHIFTIN 8 bit response code
[until response code is 0x01, keep sending CMD0]
6)8 pulse delay
7)send the init command (CMD1), which is 0x4100 0x0000 0x0000
(SHIFTOUT/MSBFIRST)
8)8 pulse delay
9)SHIFTIN 8 bit response code
[until response code is 0x00, keep sending CMD1]

At this point, the MMC should be in SPI mode and awaiting a command
to read/write a block of data.
The problem is that I can't get to that point. First, I cannot get
ANY response from the card unless I
send 21 plus a multiple of 25 clock pulses (21, 46, 71, 96, etc...).
When I do that, I can send CMD0
and loop the SHIFTIN of 8bits. This is what is (always in this order)
shifted in:
1) 0111 1110
2) 0000 0011
3) 1111 1111
4) 1111 1111
5) 1111 1111
6) 1111 1111
7) 1111 1111
8) 1111 1111
9) 1111 1110
10)0000 1011
...bytes 3 through 10 then loop indefinitely.

If, instead of looping the SHIFTIN, I continue sending CMD0 in order
to get the 0x01 response code, I never get it.
If I just continue on to issuing CMD1, the same thing happens which
is shifting in that loop of blocks 3 through 10
as if it's ignoring my CMD0 and CMD1 commands.

I think I've exhaused every PDF and HTML document I could find on the
subject and I'm hoping someone might
have had the same problem and figured it out.
ANY HELP IS APPRECIATED!!!

thanks
Jim Swensen
[jswensen*volcanomail,com]







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