sdcard, emmc, sdio, sd标准

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emmc与sd card说的是两种不同的分装， emmc是bga封装，一般焊接在板子上；而sd card为tf card/sd card的形式；注意这仅是物理的表现形式不一样！！！
而他们使用的通信接口都是SD内存卡通信标准
SDIO：SDIO是在SD卡规范间上增加了对IO设备的支持, 操作命令与sd有些不同有些相同, sd支持的叫sd card, sdio支持的叫sdio卡(如各种wifi, gps, bluetooth等)。
SD memory cards may also support a second security system based on commonly used standards,
such as ISO-7816, which can be used to interface the SD memory card into public networks and other
systems supporting mobile e-commerce and digital signature applications.
In addition to the SD Memory Card, there is the SD I/O (SDIO) Card. The SDIO Card specification is
defined in a separate specification named: "SDIO Card Specification" that can be obtained from the SD
Association. The SDIO Specification defines an SD card that may contain interfaces between various
I/O units and an SD Host. The SDIO card may contain memory storage capability as well as its I/O
functionality. The Memory portion of SDIO card shall be fully compatible to the given Physcial Layer
Specification. The SDIO card is based on and compatible with the SD Memory card. This compatibility
includes mechanical, electrical, power, signalling, and software. The intent of the SD I/O card is to
provide high-speed data I/O with low power consumption for mobile electronic devices. A primary goal is
that an I/O card inserted into a non-SDIO aware host will cause no physical damage or disruption of
that device or its software. In this case, the I/O card should simply be ignored. Once inserted into an
SDIO aware host, the detection of the card will be via the normal means described in the given Physical
Layer Specification with some extensions that are described in the SDIO Specification.
The SD Memory Card communication is based on an advanced 9-pin interface (Clock, Command,
4xData and 3xPower lines) designed to operate in at maximum operating frequency of 50 MHz and low
voltage range. The communication protocol is defined as a part of this specification.
From: SD Specifications Part 1 Physical Layer Specification Version 3.00