Specifications

©Copyright 2001-2013 SD Group (Panasonic, SanDisk, Toshiba) and SD Card Association
Physical Layer Simplified Specification Version 4.10
104
Support of CMD20 is mandatory for SDXC card and optional for SDHC card.
SDXC cards can meet Class performance when data is written after receiving CMD20 indicating the
Start Recording function. SDHC cards can meet Class performance without CMD20.
4.13.2.8.1 Definition of Each Function
(1) Start Recording
This function indicates that Speed Class host starts stream recording. When the card receives
CMD20 Start Recording function, the card indicates busy up to 1 second to prepare recording
(Garbage collection, clean-up of internal status, etc).
(2) Update DIR
This function indicates that following write command shall be a directory entry write. On receiving
CMD20 Update DIR function, the card shall recognize and manage the 512-byte area (DIR)
specified by the following single block write command (either CMD24 or CMD25) as a location of
the directory entry updated during the stream recording. The designated area (DIR) shall be written
by single block writes and may be written repeatedly without preceding CMD20 Update DIR. Write
to DIR (even without FAT write) counts in one of 8 times FAT write cycles. This function is always
needed before Start Recording. If this function is issued during the recording, the card recognizes
that the current recording is ended and the following write command is recognized as the directory
entry for the next recording. After that, the host shall issue CMD20 Start Recording to start the next
Speed Class recording. The busy indication of this function is up to 10ms for this function.
(3) Update CI
This function indicates that the following write command is a write to a CI cluster. When the card
receives CMD20 Update CI function during the recording, the card recognizes that following 512-
byte single block write (either CMD24 or CMD25) is an update to a CI cluster. Busy indication of
CMD20 Update CI is up to 10ms for this function.
4.13.2.8.2 Requirements for Speed Class Host
There are requirements for host to support CMD20
• If host records data to SDXC card, it shall support CMD20 to indicate Start Recording.
• The host shall issue CMD20 Update DIR before Start Recording regardless of updating CI
during the recording.
• If host updates CI during the recording, it shall issue CMD20 Update CI just before the 512-byte
single block write (either CMD24 or CMD25) updating CI.
4.13.2.9 Example of Speed Class Recording Sequence
Figure 4-55 shows example sequence of Speed Class recording.
Even if the write data size after CMD20 Update DIR is wrong (larger than 512-byte), the card accepts
data writes without error but Speed Class performance is not maintained.
The host starts Speed Class recording by CMD20 indicating the Start Recording function and exits by
either CMD20 indicating the Update DIR function or non-Speed Class write command. During the
recording period, allowable write operations are limited to those shown below.
1. Stream data is written by one or more RU
2. FAT Update consists of three write commands, FAT(
≤
16KB)+Bitmap(
≤
16KB)+DIR(512-byte)
3. CI Update consists of single block write (512-byte by either CMD24 or CMD25 always preceded