MMC cards in SPI mode

[markp]

Hi All,

Has anyone out there used MMC cards in SPI mode? I'm seeing a strange
problem in that I have two MMC cards with separate enable signals - if one
is enabled and the other disabled sometimes the disabled one will not
recognise a new command once it is enabled (usually returns 0x4, i.e.
invalid command). Retrying the access seems to cure it. Anyone seen anything
similar?

Thanks,

Mark.

 

[Mark VB]

Hi All,

Has anyone out there used MMC cards in SPI mode? I'm seeing a strange
problem in that I have two MMC cards with separate enable signals - if one
is enabled and the other disabled sometimes the disabled one will not
recognise a new command once it is enabled (usually returns 0x4, i.e.
invalid command). Retrying the access seems to cure it. Anyone seen anything
similar?

Thanks,

Mark.

Hi,

Because you mention that the problem only occurs after being disabled, it
seems to me that you start sending too soon. Do you use CMD58 (Read_OCR) to
check that the initialization process has completed before sending the first
command ?

2nd Possibility: Datasheets mention that, when the card encounters a data
retrieval problem, in SPI-mode it will respond with an error, rather than by
a time-out as in MMC-mode. And because none of the errors actually
corresponds to that situation... So, does the problem occur with both cards
?


Mark Van Borm

 

[markp]

Hi,

Because you mention that the problem only occurs after being disabled, it
seems to me that you start sending too soon. Do you use CMD58 (Read_OCR) to
check that the initialization process has completed before sending the first
command ?

2nd Possibility: Datasheets mention that, when the card encounters a data
retrieval problem, in SPI-mode it will respond with an error, rather than by
a time-out as in MMC-mode. And because none of the errors actually
corresponds to that situation... So, does the problem occur with both cards
?


Mark Van Borm

Hi Mark,

Initial access is OK, the problem comes when the CS* is de-asserted and then
the other card is accessed. This seems to screw up the disabled card so that
when a new command is actually given to that previously disabled card it is
decoded as illegal. (BTW CMD58 doesn't exist!). The problem seems to be only
with one card, but a retry always fixes it. Strange.

Mark.