AF512UDI Datasheet, PDF (82/91 Pages) List of Unclassifed Manufacturers – ATP Industrial Grade microSD Card Specification

Revision 3.3
ATP Industrial Grade microSD Card Specification
7 SPI Mode
7.1 Introduction
The SPI mode consists of a secondary communication protocol which is offered by SD Cards. This
mode is a subset of the SD Card protocol, designed to communicate with a SPI channel, The interface
is selected during the first reset command after power up (CMD0) and cannot be changed once the part
is powered on.
7.2 SPI BUS Topology
The ATP SD Card SPI interface is compatible with SPI hosts available on the market. As any other SPI
device the ATP SD Card SPI channel consists of the following four signals:
CS:
Host to card Chip Select signal.
CLK:
Host to card clock signal
DataIn:
Host to card data signal.
DataOut: Card to host data signal.
Another SPI common characteristic are byte transfers, which is implemented in the card as well. All
data tokens are multiples of bytes (8 bit) and always byte aligned to the CS signal.
The card identification and addressing methods are replaced by a hardware Chip Select (CS) signal.
There are no broadcast commands. For every command, a card (slave) is selected by asserting (active
low) the CS signal (see Figure 7-1).
The CS signal must be continuously active for the duration of the SPI transaction (command, response
and data). The only exception occurs during card programming, when the host can deassert the CS
signal without affecting the programming process.
The SPI interface uses the 7 out of the SD 9 signals (DAT1 and DAT 2 are not used, DAT3 is the CS
signal) of the SD bus.
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