MultiMediaCard Product Manual
20
SanDisk MultiMediaCard Product Manual Rev. 2 © 2000 SANDISK CORPORATION
DAT
CLK
1 2 3 4 5 6 7
MultiMediaCard
MultiMediaCard
Host
ROD
CMD
DAT
R
CMD
R
= max (C , C , C )
1
2
3
BUS
C
C1 C2 C3
Figure 4-1 Bus Circuitry Diagram
The R
OD
is switched on and off by the host
synchronously to the open-drain and push-pull
mode transitions. R
DAT
and R
CMD
are pull-up
resistors protecting the CMD and the DAT line
against bus floating when no card is inserted or
when all card drivers are in a hi-impedance
mode.
A constant current source can replace the R
OD
in
order to achieve a better performance (constant
slopes for the signal rising and falling edges). I f
the host does not allow the switchable R
OD
implementation, a fix R
CMD
can be used.
Consequently the maximum operating frequency in
the open drain mode has to be reduced in this case.
Hot Insertion/Removal
Hot insertion and removal are allowed. The
SanDisk MultiMediaCard will not be damaged by
inserting or removing it into the MultiMediaCard
bus even when the power is up.
•
The inserted card will be properly reset
also when CLK carries a clock frequency
f
PP
.
•
Data
transfer failures induced by
removal/insertion should be detected by
the bus master using the CRC codes which
suffix every bus transaction.
4.2.1
Power Protection
Cards can be inserted/removed into/from the bus
without damage. If one of the supply pins (V
DD
or
V
SS
)
is not connected properly, then the current is
drawn through a data line to supply the card.
Every cards output must also be able to withstand
short cuts to either supply.
If the hot insertion feature is implemented in the
host, the host has to withstand a shortcut
between V
DD
and
V
SS
without damage.
4.2.2
Programmable Card Output Driver
This option, defined in chapter 6 of the
MultiMediaCard standard, is not implemented in
the SanDisk MultiMediaCard.
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