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SMS01GAF Datasheet(PDF) 44 Page - Numonyx B.V |
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SMS01GAF Datasheet(HTML) 44 Page - Numonyx B.V |
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44 / 61 page ![]() Serial peripheral interface (SPI) mode SMSxxxAF, SMSxxxFF, SMSxxxBF 44/61 7.2.2 Bus Transfer Protection On entering the SPI mode the card defaults to the non-protected mode where there is no CRC (Cyclic Redundancy Check). So systems using reliable data links are not obliged to have the hardware and firmware necessary to implement CRC functions. In non-protected mode, the CRC bits are still present but are Don't Care. The CRC option can be turned on and off by the host through the CRC_ON_OFF command (CMD59). 7.2.3 Data Read Single and Multiple Block Read operations are supported in SPI mode. The main difference with the SD mode is that in SPI mode data and responses to the host are both sent on the DataOut line. As a consequence the data transfer may be interrupted and the last data block, replaced by the response to a STOP_TRANSMISSION command. The basic unit of data transfer is the block. The maximum size of a block is defined in the CSD Register (READ_BL_LEN). If READ_BL_PARTIAL is set, smaller blocks entirely contained in a physical block (as defined by READ_BL_LEN) may also be transmitted. Single Block Read operations are initiated by issuing the READ_SINGLE_BOCK command (CMD17). The start address can be any Byte in the valid address range of the card. Every block, however, must be contained in a single physical card sector. Multiple Block Read operations are initiated by issuing the READ_MULTIPLE_BLOCK command (CMD18) and every transferred block has a 16-bit CRC appended to it. The STOP_TRANSMISSION command (CMD12) will actually stop the data transfer operation (just like in the SD mode). Figure 32. Read Operation Mechanism Figure 33. Multiple Block Read Operation Command Command Data in Data out ai10066 from Card to Host from Host to Card next command Response Data Block CRC data from Card to Host Command STOP_TRANSMISSION Command Data in Data out ai10067 from Card to Host from Host to Card next command Response Data Block CRC data from Card to Host Data Block CRC Data B. Response |
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