User Manual

Secure Digital (SD) Bus Protocol Description

4-17

4.7. Error Conditions

The following sections provide valuable information for TriFlash error conditions.

4.7.1. CRC and Illegal Command

All commands are protected by CRC bits. If the addressed TriFlash device’s CRC check fails, the device does not

respond and the command is not executed. The TriFlash does not change its state, and COM_CRC_ERROR bit is

set in the status register.

Similarly, if an illegal command has been received, a TriFlash 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 4-7 and Figure 4-8). Table 4-12 contains a complete state transition description.

There are different kinds of illegal commands:

• Commands that belong to classes not supported by the TriFlash (e.g., write commands in read-only

devices).

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

• Commands that are 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 (device 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 (device independent) either 100 times longer than the typical

program times for these operations given below or 250ms. A device 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 device is not going to respond anymore and try to recover (e.g., reset the device, 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 device 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.

4.8. Commands

The following sections provide valuable information for TriFlash commands.