GD32W51x User Manual
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register shall be set in the factory by the SD Memory Card manufacturer. The host can use
ACMD51 to get the content of this register.
23.5.2.
Commands
Commands types
There are four kinds of commands defined to control the Card:
Broadcast commands (bc), no response
Broadcast commands with response (bcr) response from all cards simultaneously
Addressed (point-to-point) commands (ac) no data transfer on D
Addressed (point-to-point) data transfer commands (adtc) data transfer on D
Command format
All commands have a fixed code length of 48 bits, as show in
, needing a transmission time of 1.92μs (25 MHz) 0.96μs (50 MHz) and 0.92us (52
MHz).
Figure 23-7. Command Token Format
0
1
Content
CRC
1
Total length = 48 bits
Table 23-2. Command format
Bit position
47
46
[45:40]
[39:8]
[7:1]
0
Width
1
1
6
32
7
1
Value
‘0’
‘1’
x
x
x
‘1’
Description
start bit
transmission bit
command index
argument
CRC7
end bit
A command always starts with a start bit (always 0), followed by the bit indicating the direction
of transmission (host = 1). The next 6 bits indicate the index of the command, this value being
interpreted as a binary coded number (between 0 and 63). Some commands need an
argument (e.g. an address), which is coded by 32 bits. A value denoted by
‘
x
’
in the table
above indicates this variable is dependent on the command. All commands are protected by
a CRC7. Every command code word is terminated by the end bit (always 1).
Command classes
The command set of the Card system is divided into several classes (See
). Each class supports a set of card functionalities.
determines the setting of CCC from the card supported
commands.
For SD cards, Class 0, 2, 4, 5 and 8 are mandatory and shall be supported. Class 7 except