User Manual

Secure Digital (SD) Bus Protocol Description

All timing diagrams use the schematics and abbreviations listed in Table 4-1.

Table 4-1. Timing Diagram Abbreviations

H Signal is high (logical ‘1’)

L Signal is low (logical ‘0’)

X Do not care

Z High impedance state (-> = 1)

* Repeater

Busy Busy Token

Command Command token

Response Response token

Data block Data token

4.2. Protocol’s Functional Description

All communication between the host and TriFlash devices is controlled by the host (master). The host sends

commands of two types: broadcast and addressed (point-to-point) commands.

• Broadcast Commands—Broadcast commands are intended for all TriFlash devices and SD cards.

Some of these commands require a response.

• Addressed (Point-to-Point) Commands—The addressed commands are sent to the addressed

TriFlash and cause a response to be sent from this device.

A general overview of the command flow is shown in Figure 4-7 for the Card Identification Mode and in Figure 4-8

for the Data Transfer Mode. The commands are listed in the command tables (Table 4-4 through Table 4-11). The

dependencies between the current SD bus state, received command and following state are listed in Table 4-2. In the

following sections, the different device operation modes will be described first. Thereafter, the restrictions for

controlling the clock signal are defined. All SD bus commands together with the corresponding responses, state

transitions, error conditions and timings are presented in the following sections.

Two operation modes are defined for SD bus devices:

• Card Identification Mode—The host will be in card identification mode after reset and while it is

looking for new devices on the bus. TriFlash devices will be in this mode after reset until the

SEND_RCA command (CMD3) is received.

• Data Transfer Mode—TriFlash devices will enter data transfer mode once their RCA is first

published. The host will enter data transfer mode after identifying all of the devices on the bus.