Chapter 1 – Introduction
Revision 2.2
SanDisk SD Card Product Manual
© 2004 SanDisk Corporation
1-9
12/08/04
1.12.8
Data Protection in the Flash Card
Every sector is protected with an error correction code (ECC). The ECC is generated (in
the memory card) when the sectors are written and validated when the data is read. If
defects are found, the data is corrected prior to transmission to the host.
1.12.9 Write
Protection
Two-card level write-protection options are available: permanent and temporary. Both can
be set using the PROGRAM_CSD command (refer to
CSD Programming
). The permanent
write-protect bit, once set, cannot be cleared. This feature is implemented in the SD Card
controller firmware and not with a physical OTP cell.
Use the Write Protect (WP) Switch located on the card’s side edge to prevent the host from
writing to or erasing data on the card. The WP switch does not have any influence on the
internal Permanent or Temporary WP bits in the CSD Register.
1.12.10 Copy
Bit
The copy bit can be used to mark an SD Card content as an original or a copy. The copy
bit of the card is programmed as a copy when testing and formatting are performed during
manufacturing. When set, the copy bit in the CSD Register is a copy and cannot be cleared.
The card is available with the copy-bit set or cleared. If the bit is set, it indicates that the
card is a master. This feature is implemented in the card’s controller firmware and not with
a physical OTP cell.
1.12.11 CSD
Register
All SD Card configuration information is stored in the CSD Register. The MSB bytes of
the register contain manufacturer data and the two least significant bytes contain the host-
controlled data: the card copy/write protection, and the user file format.
The host can read the CSD Register and alter the host-controlled data bytes using the
SEND_CSD and PROGRAM_CSD commands.
1.13 SPI
Mode
The SPI mode is a secondary communication protocol for SD cards. This mode is a subset
of the SD Protocol, designed to communicate with an SPI channel, commonly found in
Motorola and other vendors’ microcontrollers.
Table 1-3
SPI Mode
Function Description
Negotiating Operating Conditions
The operating condition negotiation function of the SD Card bus
is supported differently in SPI mode by using the READ_OCR
(CMD58) command. The host works within the valid voltage
range (2.7 to 3.6 v) of the card or put the card in inactive state
by sending a GO_INACTIVE command to the card.
Card Acquisition and Identification
The host must know the number of cards currently connected on
the bus. Specific card selection is done via the CS signal
(CD/DAT3). The internal pull-up resistor on the CD/DAT3 line
may be used for card detection (insertion/removal). Additional
practical card detection methods can be found in SD Physical
Specification’s Application Notes given by the SDA.