SDIO interface (SDIO) RM0008
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19.5.5 R4 (Fast I/O)
Code length: 48 bits. The argument field contains the RCA of the addressed card, the
register address to be read out or written to, and its content.
19.5.6 R4b
For SD I/O only: an SDIO card receiving the CMD5 will respond with a unique SDIO
response R4. The format is:
Table 126. R3 response
Bit position Width (bits Value Description
47 1 0 Start bit
46 1 0 Transmission bit
[45:40] 6 ‘111111’ Reserved
[39:8] 32 X OCR register
[7:1] 7 ‘1111111’ Reserved
0 1 1 End bit
Table 127. R4 response
Bit position Width (bits Value Description
47 1 0 Start bit
46 1 0 Transmission bit
[45:40] 6 ‘111111’ Reserved
[39:8] Argument field
[31:16] 16 X RCA
[15:8] 8 X register address
[7:0] 8 X read register contents
[7:1] 7 ‘1111111’ CRC7
0 1 1 End bit
Table 128. R4b response
Bit position Width (bits Value Description
47 1 0 Start bit
46 1 0 Transmission bit
[45:40] 6 x Reserved
[39:8] Argument field
39 16 X Card is ready
[38:36] 3 X Number of I/O functions
35 1 X Present memory
[34:32] 3 X Stuff bits
[31:8] 24 X I/O ORC
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