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1-Bit SD Interface
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SWRU543–January 2019
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SD Host Controller Interface
Figure 11-1. SDHost Controller Interface Block Diagram
The interface uses three signal lines to communicate with the SD card:
• CLK: Generated internally by the SD host controller and provided to the external SD card
• CMD: Bidirectional; used to send commands and receive responses
• DATA: Bidirectional; used to send and receive data to and from the attached SD card
The bus protocol between the SD host controller and the card is message-based. Each message is
represented by one of the following parts:
• Command: A command starts an operation. The command is transferred serially from the SD host
controller to the card on the CMD line.
• Response: A response is an answer to a command. The response is sent from the card to the SD
host controller, and is transferred serially on the CMD line.
• Data: Data is transferred from the SD host controller to the card, or from a card to the SD host
controller, using the DATA line.
• Busy: The data signal is maintained low by the card, as it programs the data received.
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