SanDisk SD128, SD064, SD032 manual SanDisk SD-ROM Card Functional Description

2 SanDisk SD-ROM Card Functional Description

SanDisk SD-ROM Cards are compatible with the SD specifications, with some changes necessary for a read-only memory.

In an SD host system, the host controls all communication between itself and the cards. For detailed information, refer to Section 4 of the SDA Physical Layer Specification, Version 2.00.

This chapter contains the functional description for SanDisk SD-ROM Cards.

2.1 SD Bus Protocol

Communication over the SD bus is based on command and data-bit streams initiated by a start bit and terminated by a stop bit. See Section 3.6.1 of the SDA Physical Layer Specification, Version 2.00, for details.

2.2 SPI Mode

The SPI Mode is a secondary communication protocol for cards in the SanDisk SD-ROM Cards. This interface mode is an alternate to the SD protocol and is designed to communicate with an SPI channel, commonly found in Motorola and other vendors' microcontrollers. More information about SPI Mode can be found in Section 7 of the SDA Physical Layer Specification, Version 2.00.

2.3 Cyclic Redundancy Codes

Cyclic Redundancy Codes (CRC) protect against transmission errors that may occur on the bus in SD systems. Detailed information and examples for CRC7 and CRC16 are provided in Section 4.5 of the SDA Physical Layer Specification, Version 2.00.

2.4 Clock Control

The host can use the bus clock signal to SanDisk SD-ROM Cards to decrease power consumption or to control data flow on the bus. See Section 4.4 of the SDA Physical Layer Specification, Version 2.00.

2.5 Sleep Mode

SanDisk SD Cards implement a feature to automatically enter and exit from sleep mode. Upon completion of an operation, cards enter sleep mode to conserve power if no additional commands are received in less than 5 milliseconds (ms). The host does not have to take any action for this to occur; however, in order to achieve the lowest sleep current, the host should also shut down its clock to the card. In most systems, cards are in sleep mode except when accessed by the host, thus conserving power.

When the host is ready to access a card in sleep mode, any command issued to the card will cause it to exit sleep mode and respond.

2.6 Hot Insertion

SanDisk SD-ROM Cards support hot insertion into a powered host device through SD connectors that have power pins that make contact before the signal pins. This approach is similar to that used in PCMCIA and MMCA devices to allow for hot insertion. For more information, refer to Section 6.1 and Section 6.2 of the SDA Physical Layer Specification, Version 2.00.

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