User Manual

SPI Protocol Definition
5-2 TriFlash with SD Interface Product Manual (Preliminary), Rev. 1.2 © 2002/2003 SANDISK CORPORATION
5.1.2. Bus Transfer Protection
Every TriFlash token transferred on the bus is protected by CRC bits. In SPI mode, the TriFlash offers a non-
protected mode, which enables systems built with reliable data links to exclude the hardware or firmware required
for implementing the CRC generation and verification functions.
In the non-protected mode the CRC bits of the command, response and data tokens are still required in the tokens
however, they are defined as “do not cares” for the transmitters and ignored by the receivers.
The SPI interface is initialized in the non-protected mode. The host can turn this option on and off using
CRC_ON_OFF command (CMD59).
The CRC7/CRC16 polynomials are identical to that used in SD Bus mode. Refer to this section in the SD Bus Mode
Section.
5.1.3. Data Read
SPI mode supports single block and multiple block read operations (CMD17 or CMD18). Upon reception of a valid
read command the device will respond with a response token followed by a data token in the length defined in a
previous SET_BLOCK_LENGTH (CMD16) command (see Figure 5-1).
From
Host to
Card
From
Card to
Host
DataIn
DataOut
Command
Response
Data Block CRC
Data from
Card to Host
Next
Command
Command
Figure 5-1. Single Block Read Operation
A valid data block is suffixed with a 16 bit CRC generated by the standard CCITT polynomial:
x
16
+x
12
+x
5
+1.
The maximum block length is 512 bytes as defined by READ_BL_LEN (CSD parameter). Block lengths can be any
number between 1 and READ_BL_LEN.
The start address can be any byte address in the valid address range of the device. Every block, however, must be
contained in a single physical device sector.
In case of data retrieval error, the device will not transmit any data. Instead, a special data error token will be sent to
the host. Figure 5-2 shows a data read operation that terminated with an error token rather than a data block.