•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 kΩ internal pull-up resistor is too large.

•MMCDAT: Bidirectional data channel, operating in push-pull mode.

5.13.2Secure 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.

LZT 123 1836

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