DEVICE OVERVIEW
The e?MMC? device transfers data via a configurable number of data bus signals. The communication signals are:
CLK
Each cycle of this signal directs a one bit transfer on the command and either a one bit (1x) or a two bits transfer (2x)
on all the data lines. The frequency may vary between zero and the maximum clock frequency.
Data Strobe
This signal is generated by the device and used for output in HS400 mode. The frequency of this signal follows the
frequency of CLK. For data output each cycle of this signal directs two bits transfer(2x) on the data - one bit for positive
edge and the other bit for negative edge. For CRC status response output and CMD response output (enabled only HS400
enhanced strobe mode), the CRC status and CMD Response are latched on the positive edge only, and don't care on the
negative edge.
CMD
This signal is a bidirectional command channel used for device initialization and transfer of command. The CMD
signal has two operation modes: open-drain for initialization mode, and push-pull for fast command transfer.
Command are sent from the e?MMC? host controller to the e?MMC? device and responses are sent from the device to the
host.
DAT0-DAT7
These are bidirectional data channels. The DAT signals operate in push-pull mode. Only the device or the host is
driving these signals at a time. By default, after power up or reset, only DAT0 is used for data transfer. A wider data bus can
be configured for data transfer, using either DAT0-DAT3 or DAT0-DAT7, by the e?MMC? host controller. The e?MMC?
device includes internal pull-ups for data lines DAT1-DAT7. Immediately after entering the 4-bit mode, the device
disconnects the internal pull ups of lines DAT1, DAT2, and DAT3. Correspondingly, immediately after entering to the 8-bit
mode the device disconnects the internal pull-ups of lines DAT1–DAT7.
