SanDisk SDMB-16-771 Product Manual - Page 14

MultiMediaCard Product Manual The MultiMediaCard supports three read/write 1.5.8.8 modes as shown in the above figure. Erase Stream Mode In stream mode the host reads or writes continues stream of data. The starting address is specified in the read/write command and the operation ends when the host sends a stop transmission command. The smallest erasable unit in t h e MultiMediaCard is a sector. In order to speed up the erase procedure, multiple sectors can be erased in the same time. The erase operation is divided into two stages: In this mode there is no validity check on t h e transferred data. The start address for a read operation can be any random byte address in the valid address space of the memory card. For a write operation, the start address must be sector aligned and the data length must be an integer multiplication of the sector length. Single Block Mode In this mode the host reads or writes one data block in a pre-specified length. The data block transmission is protected with 16 bit CRC which is generated by the sending unit and checked by the receiving unit. The block length, for read operations, is limited by the device sector size (512 bytes) but can be as small as a single byte. Misalignment is not allowed. Every data block must be contained in a single physical sector. Tagging - Selecting the Sectors for Erasing To facilitate selection, a first command with t h e starting address is followed by a second command with the final address, and all sectors within this range will be selected for erase. After a range is selected, individual sectors (or groups) within that range can be removed using the UNTAG command. Erasing - Starting the Erase Process The sectors are grouped into erase groups of 16 or 32 sectors. Tagging can address sectors or erase groups. Either an arbitrary set of sectors within a single erase group, or an arbitrary selection of erase groups may be erased at one time, but not both together. That is, the unit of measure for determining an erase is either a sector or an erase group, but if a sector, all selected sectors must l i e within the same erase group. Tagging and erasing sectors must follow a strict command sequence. The block length for write operations must be identical to the sector size and the start address aligned to a sector boundary. Multiple Block Mode This mode is similar to the single block mode, but the host can read/write multiple data blocks ( a l l have the same length) which will be stored or retrieved from contiguous memory addresses starting at the address specified in the command. The operation is terminated with a stop transmission command. Misalignment and block length restrictions apply to multiple blocks as well and are identical to t h e single block read/write operations. 1.5.8.7 Data Protection in the Flash Card 1.5.8.9 Write Protection The MultiMediaCard erase groups are grouped into write protection groups. Commands are provided for limiting and enabling write and erase privileges for each group individually. The current write protect map can be read using t h e SEND_WRITE_PROT command. In addition two, permanent and temporary, card level write protection options are available. Both can be set using the PROGRAM_CSD command (see below). The permanent write protect bit, once set, cannot be cleared. This feature is implemented in the MultiMediaCard controller firmware and not with a physical OTP cell. 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, t h e data is corrected prior to transmission to the host. 14 SanDisk MultiMediaCard Product Manual Rev. 2 © 2000 SANDISK CORPORATION