LZT 123 1836
62
•
MMCCMD: Bidirectional command channel that initializes a card and transfers
commands. CMD has two operational modes; open-drain for initialization and
push-pull for command transfer. This depends on speed requirements for the
command channel during the initialization phase; external open-drain pull-up
resistor may be needed if the 200 k
Ω
internal pull-up resistor is too large.
•
MMCDAT: Bidirectional data channel, operating in push-pull mode.
5.13.2
Secure Digital Memory Card System
The secure digital memory card system consists of the host and cards connected in a
star topology. Multimedia cards and secure digital memory cards can be used in the
same system. The power supply can be provided by the host or level-shifter devices
such as Agere’s PSC2217.
The following signals are used on the secure digital memory card bus:
•
MMCCLK: Host to card clock signal.
•
MMCCMD: Bidirectional command/response signal (one per card if multiple cards
are connected to the bus, in which case, bus multiplexing logic is required).
•
MMCDAT[3:0]: Bidirectional data signals (one set per card).
•
VDD, VSS: Power and ground signals provided by the host or level translator
product.
The MCI (Multimedia Card Interface) does not contain bus multiplexing logic. If more
than one secure digital memory cards needs to be supported, the user must
implement bus multiplexing logic with external components.
