8. The eMMC bus

The eMMC bus has eleven communication lines and three supply lines:



CMD: Command is a bidirectional signal. The host and Device drivers are operating in two modes,

open drain and push/pull.



DAT0-7: Data lines are bidirectional signals. Host and Device drivers are operating in push-pull

mode.



CLK: Clock is a host to Device signal. CLK operates in push-pull mode.



Data Strobe: Data Strobe is a Device to host signal. Data Strobe operates in push-pull mode.

Figure 10: Bus Circuitry Diagram

The ROD is switched on and off by the host synchronously to the open-drain and push-pull mode transitions.

The host does not have to have open drain drivers, but must recognize this mode to switch on the ROD. RDAT

and RCMD are pull-up resistors protecting the CMD and the DAT lines against bus floating device when all device

drivers are in a high-impedance mode.

A constant current source can replace the ROD by achieving a better performance (constant slopes for the signal

rising and falling edges). If the host does not allow the switchable ROD implementation, a fixed RCMD can be

used). Consequently the maximum operating frequency in the open drain mode has to be reduced if the used

RCMD value is higher than the minimal one given in.

RData strobe is pull-down resistor used in HS400 device.

Confidential

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Rev.1.0 July 2023

32GB/64GB/128GB eMMC