Product manual

Secure Digital (SD) Card Protocol Description

4.7. Error Conditions

The following sections provide valuable information on error conditions.

4.7.1. CRC and Illegal Command

All commands are protected by CRC bits. If the addressed Industrial Grade SD Card’s CRC check fails, the card

does not respond and the command is not executed. The Industrial Grade SD Card does not change its state, and

COM_CRC_ERROR bit is set in the status register.

Similarly, if an illegal command has been received, an Industrial Grade SD Card shall not change its state, shall not

respond and shall set the ILLEGAL_COMMAND error bit in the status register. Only the non-erroneous state

branches are shown in the state diagrams (Figure 5-7 and Figure 5-8). Table 5-11 contains a complete state

transition description.

There are different kinds of illegal commands:

• Commands belonging to classes not supported by the SD Card (e.g., write commands in read-only

cards).

• Commands not allowed in the current state (e.g., CMD9 in Transfer State).

• Commands not defined (e.g., CMD5).

4.7.2. Read, Write and Erase Time-out Conditions

The times after which a time-out condition for Read operations occur are (card independent) either 100 times

longer than the typical access times for these operations given below or 100ms. The times after which a time-out

condition for Write/Erase operations occur are (card independent) either 100 times longer than the typical program

times for these operations given below or 250ms. A card shall complete the command within this time period, or

give up and return an error message. If the host does not get any response with the given time out it should assume

the card is not going to respond anymore and try to recover (e.g., reset the card, power cycle, reject). The typical

access and program times are defined as follows:

Read

The read access time is defined as the sum of the two times given by the CSD parameters TAAC and NSAC. These

card parameters define the typical delay between the end bit of the read command and the start bit of the data block.

Write

The R2W_FACTOR field in the CSD is used to calculate the typical block program time obtained by multiplying

the read access time by this factor. It applies to all write/erase commands (e.g., SET(CLEAR)_WRITE_PROTECT,

PROGRAM_CSD(CID) and the block write commands).

Erase

The duration of an erase command will be (order of magnitude) the number of write blocks (WRITE_BL) to be

erased multiplied by the block write delay.