Specifications

©Copyright 2001-2013 SD Group (Panasonic, SanDisk, Toshiba) and SD Card Association
Physical Layer Simplified Specification Version 4.10
59
4.3.13 Send Interface Condition Command (CMD8)
CMD8 (Send Interface Condition Command) is defined to initialize SD Memory Cards compliant to the
Physical Layer Specification Version 2.00 or later. CMD8 is valid when the card is in Idle state. This
command has two functions.
• Voltage check:
Checks whether the card can operate on the host supply voltage.
• Enabling expansion of existing command and response:
Reviving CMD8 enables to expand new functionality to some existing commands by redefining
previously reserved bits. ACMD41 was expanded to support initialization of SDHC Card and
the expansion is also applied to SDXC Card.
Table 4-18 shows the format of CMD8.
Voltage Supplied
Value Definition
0000b
Not Defined
0001b
2.7-3.6V
0010b
Reserved for Low Voltage Range
0100b
Reserved
1000b
Reserved
Others
Not Defined
Table 4-18: Format of CMD8
When the card is in Idle state, the host shall issue CMD8 before ACMD41. In the argument, 'voltage
supplied' is set to the host supply voltage and 'check pattern' is set to any 8-bit pattern.
The card checks whether it can operate on the host's supply voltage. The card that accepted the
supplied voltage returns R7 response. In the response, the card echoes back both the voltage range
and check pattern set in the argument. If the card does not support the host supply voltage, it shall not
return response and stays in Idle state.
A part of this section is not described.
Table 4-19: A Blank in the Simplified Specification
Bit position
47
46
[45:40]
[39:20]
[19:16]
[15:8]
[7:1]
0
Width (bits)
1
1
6
20
4
8
7
1
Value
'0'
'1'
'001000'
'00000h'
x
x
x
'1'
Description
Start
bit
Transmission
bit
Command
index
Reserved
bits
Voltage
supplied
(VHS)
Check
pattern
CRC7
End bit