Table 112. Data Types - STMicroelectronics STM32F405 Reference Manual

RM0090
The system memory organization is little-endian: whatever the data type (bit, byte, 16-bit
half-word, 32-bit word) used, the least-significant data occupy the lowest address locations.
A bit, byte, or half-word swapping operation (depending on the kind of data to be encrypted)
therefore has to be performed on the data read from the IN FIFO before they enter the
CRYP processor. The same swapping operation should be performed on the CRYP data
before they are written into the OUT FIFO. For example, the operation would be byte
swapping for an ASCII text stream.
The kind of data to be processed is configured with the DATATYPE bitfield in the CRYP
control register (CRYP_CR).
DATATYPE in
Swapping performed
CRYP_CR
00b
01b
10b
11b
Figure 229
bit words popped off the IN FIFO by the CRYP processor, according to the DATATYPE
value. The same schematic can easily be extended to form the 128-bit block for the AES

Table 112. Data types

No swapping
Half-word (16-bit)
swapping
Byte (8-bit) swapping
Bit swapping
shows how the 64-bit data block M1...64 is constructed from two consecutive 32-
DocID018909 Rev 11
System memory data
(plaintext or cypher)
Example: TDES block value
represented in system memory as:
Example: TDES block value 0xABCD77206973FE01 is
represented in system memory as:
Example: TDES block value 0xABCD77206973FE01 is
represented in system memory as:
TDES block value 0x4E6F772069732074
memory as:
Cryptographic processor (CRYP)
0xABCD77206973FE01
is represented in system
is
731/1731
757