Cypress Semiconductor CY8C21534 Spezifikationen PDF herunterladen (Seite 14)

2.3 SD Card Command Format

There are two different modes of communication through the data lines of the SD

memory card. The usual method used by host devices is the SD Bus mode, also called

the SD mode. The other method is the SPI mode. Both modes have similar protocols

but the SD mode allows for multiple data lines operating simultaneously. The SPI

mode is slower than the SD mode but it is easier to implement and it is a well known

interface.

The commands for using the SPI mode of the SD card consist of six bytes which give

the SD card the information it needs to perform the required task. In figure 5 the

command 0, which is used to initialize the card into the SPI mode, can be seen as given

by the PSoC microcontroller over SPI connection.

Figure 5: PSoC Designer SPI CMD 0. Screenshot [3].

The first byte, called the command byte, is made by converting the command number

from a decimal value to a hex value and then adding a hex value of 0x40. Figure 5

shows a command number of 0 added to 0x40 which would give an argument of

0x40. Another example could be the command 55. First the command number 55

would be changed to a hex 0x37 and then added to a hex 0x40 to give a command

byte of 0x77.

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Cypress Semiconductor CY8C21534 Spezifikationen Seite 14