SanDisk SD Card

Revision 2.2Chapter 1 – IntroductionSanDisk SD Card Product Manual1.12.8 Data Protection in the Flash CardEvery sector is protected with an error correction code (ECC). The ECC is generated (inthe memory card) when the sectors are written and validated when the data is read. Ifdefects are found, the data is corrected prior to transmission to the host.1.12.9 Write ProtectionTwo-card level write-protection options are available: permanent and temporary. Both canbe set using the PROGRAM_CSD command (refer to CSD Programming). The permanentwrite-protect bit, once set, cannot be cleared. This feature is implemented in the SD Cardcontroller 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 fromwriting to or erasing data on the card. The WP switch does not have any influence on theinternal Permanent or Temporary WP bits in the CSD Register.1.12.10 Copy BitThe copy bit can be used to mark an SD Card content as an original or a copy. The copybit of the card is programmed as a copy when testing and formatting are performed duringmanufacturing. 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 thecard is a master. This feature is implemented in the card’s controller firmware and not witha physical OTP cell.1.12.11 CSD RegisterAll SD Card configuration information is stored in the CSD Register. The MSB bytes ofthe register contain manufacturer data and the two least significant bytes contain the hostcontrolleddata: 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 theSEND_CSD and PROGRAM_CSD commands.1.13 SPI ModeThe SPI mode is a secondary communication protocol for SD cards. This mode is a subsetof the SD Protocol, designed to communicate with an SPI channel, commonly found inMotorola and other vendors’ microcontrollers.Table 1-3 SPI ModeFunctionNegotiating Operating ConditionsCard Acquisition and IdentificationDescriptionThe operating condition negotiation function of the SD Card busis supported differently in SPI mode by using the READ_OCR(CMD58) command. The host works within the valid voltagerange (2.7 to 3.6 v) of the card or put the card in inactive stateby sending a GO_INACTIVE command to the card.The host must know the number of cards currently connected onthe bus. Specific card selection is done via the CS signal(CD/DAT3). The internal pull-up resistor on the CD/DAT3 linemay be used for card detection (insertion/removal). Additionalpractical card detection methods can be found in SD PhysicalSpecification’s Application Notes given by the SDA.© 2004 SanDisk Corporation 1-9 12/08/04