SD2.0协议详解：高容量、性能提升与兼容性特点

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SD卡2.0协议，全称为Secure Digital 2.0或SDHC协议，是SD卡协会为提升存储卡性能和容量而制定的一项标准。相比于最初的SD1.0协议，SD2.0协议具有显著的改进： 1. 高容量支持：SD2.0协议的最大存储容量提升至32GB，相较于SD1.0的2GB有了质的飞跃，这对于需要大量存储空间的应用场景如摄影、视频录制和游戏等非常关键。 2. 文件系统支持：新协议引入了FAT32文件系统，这是一种更高效的文件管理系统，能够更好地组织和管理大容量存储空间中的文件，方便用户查找和访问。 3. 性能增强：SD2.0协议提高了数据传输速度，最高可达25MB/s，显著提升了读写速度，这对于处理大量数据或者实时传输时至关重要。这使得SD卡在高清摄影、高速下载或多媒体应用中表现出色。 4. 兼容性：尽管SD2.0引入了新特性，但它仍保持了向下兼容，也就是说，SD2.0卡片可以被旧版SD1.0设备读取，但其实际可用容量会受限于设备支持的版本。这是为了确保广泛设备间的互操作性。 5. 技术细节：SD2.0协议的详细规格由SD卡协会发布，由多个公司参与，包括松下（Matsushita Electric Industrial Co., Ltd.，现Panasonic）、SanDisk和东芝等。协议的修订历史反映了技术的进步，如2006年9月发布的2.00版本是对1.10版本的更新和完善。 SD卡2.0协议是存储卡技术的重要里程碑，它不仅解决了容量瓶颈，还提升了用户体验。对于任何需要高效存储和快速数据传输的用户，选择符合SD2.0标准的卡片将是明智的选择。随着技术的发展，后续的SD3.0、SD4.0等版本将进一步优化性能和功能。

Physical Layer Simplified Specification Version 2.00

3. SD Memory Card System Concept

Description here is a blank for the Simplified Specification.

3.1 Read-Write Property

In terms of read-write property, two types of SD Memory Cards are defined:

• Read/Write (RW) cards (Flash, One Time Programmable - OTP, Multiple Time Programmable -

MTP). These cards are typically sold as blank (empty) media and are used for mass data storage,

end user video, audio or digital image recording

• Read Only Memory (ROM) cards. These cards are manufactured with fixed data content. They are

typically used as a distribution media for software, audio, video etc.

3.2 Supply Voltage

In terms of operating supply voltage, two types of SD Memory Cards are defined:

• High Voltage SD Memory Cards that can operate within the voltage range of 2.7-3.6 V.

• Dual Voltage SD Memory Cards –Dual Voltage SD Memory Cards that can operate within the

voltage range of Low Voltage Range (T.B.D) and 2.7-3.6 V.

Note that details of Dual Voltage SD Memory Card will be defined in future specification.

3.3 Card Capacity

In terms of capacity, two types of SD Memory Cards are defined:

• Standard Capacity SD Memory Cards supports capacity up to and including 2 G bytes (2

bytes).

All versions of the Physical Specifications define the Standard Capacity SD Memory Card.

• High Capacity SD Memory Cards supports capacity more than 2 G bytes (2

bytes) and this version

of specification limits capacity up to and including 32 GB. High Capacity SD Memory Card is newly

defined from the Physical Layer Specification Version 2.00.

Only hosts that are compliant to the Physical Layer Specification version 2.00 or higher and the SD File

System Specification Ver2.00 can access High Capacity SD Memory Cards. Other hosts fail to initialize

High Capacity SD Memory Cards (See Figure 3-1).

Note:

1. The Part 1 Physical Layer Specification Version 2.00 and Part 2 File System Specification

Version 2.00 allow Standard Capacity SD Memory Cards to have capacity up to and

including 2 GB and High Capacity SD Memory Cards to have capacity up to and including

32 GB. SD Memory Cards with a capacity greater than 32 GB will be available with updated

versions of Part 1 and Part 2 Specifications.

2. Hosts that can access (read and/or write) SD Memory Cards with a capacity greater than 2

GB and up to and including 32 GB, shall also be able to access SD Memory Cards with a

capacity of 2 GB or less.

Physical Layer Simplified Specification Version 2.00

3.5 Bus Topology

This section is a blank for the Simplified Specification.

3.6 Bus Protocol

3.6.1 SD Bus

Communication over the SD bus is based on command and data bit streams that are initiated by a start

bit and terminated by a stop bit.

• Command: a command is a token that starts an operation. A command is sent from the host either

to a single card (addressed command) or to all connected cards (broadcast command). A command

is transferred serially on the CMD line.

• Response: a response is a token that is sent from an addressed card, or (synchronously) from all

connected cards, to the host as an answer to a previously received command. A response is

transferred serially on the CMD line.

• Data: data can be transferred from the card to the host or vice versa. Data is transferred via the

data lines.

Figure 3-2: “no response” and “no data” Operations

Card addressing is implemented using a session address, assigned to the card during the initialization

phase. The structure of commands, responses and data blocks is described in Chapter 4. The basic

transaction on the SD bus is the command/response transaction (refer to Figure 3-2). This type of bus

transaction transfers their information directly within the command or response structure. In addition,

some operations have a data token.

Data transfers to/from the SD Memory Card are done in blocks. Data blocks are always succeeded by

CRC bits. Single and multiple block operations are defined. Note that the Multiple Block operation mode

is better for faster write operation. A multiple block transmission is terminated when a stop command

follows on the CMD line. Data transfer can be configured by the host to use single or multiple data lines.

command response

block read operation

data stop operation

CMD

DAT

from

host

to card

stop command

stops data transfer

data from card

to host

from

card

to host

data block crc

data block crc data block crc

multiple block read operation

Figure 3-3: (Multiple) Block Read Operation

The block write operation uses a simple busy signaling of the write operation duration on the DAT0 data

line (see Figure 3-4) regardless of the number of data lines used for transferring the data.

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