GD32F403xx User Manual
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length, transfer rate or number of cards). The CSD register carries the information about the
DSR register usage. The default value of the DSR register is 0x404. The host can use CMD4
to get the content of this register.
SCR register
: Just SD/SD I/O (if has memory port) have this register. In addition to the CSD
register, there is another configuration register named SD CARD Configuration Register
(SCR), which is only for SD card. SCR provides information on the SD Memory Card's special
features that were configured into the given card. The size of SCR register is 64 bits. This
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.
20.5.2.
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 DAT
◼
Addressed (point-to-point) data transfer commands (adtc) data transfer on DAT
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 20-7. Command Token Format
0
1
Content
CRC
1
Total length = 48 bits
Table 20-2. 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