RM0090: Reference manual - STMicroelectronics

CRC calculation unit RM0090
4 CRC calculation unit
This section applies to the whole STM32F4xx family, unless otherwise specified.
4.1 CRC introduction
The CRC (cyclic redundancy check) calculation unit is used to get a CRC code from a 32-bit
data word and a fixed generator polynomial.
Among other applications, CRC-based techniques are used to verify data transmission or
storage integrity. In the scope of the EN/IEC 60335-1 standard, they offer a means of
verifying the Flash memory integrity. The CRC calculation unit helps compute a signature of
the software during runtime, to be compared with a reference signature generated at linktime
and stored at a given memory location.
4.2 CRC main features
● Uses CRC-32 (Ethernet) polynomial: 0x4C11DB7
– X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 +X8 + X7 + X5 + X4 + X2 + X +1
● Single input/output 32-bit data register
● CRC computation done in 4 AHB clock cycles (HCLK)
● General-purpose 8-bit register (can be used for temporary storage)
The block diagram is shown in Figure 6.
Figure 6. CRC calculation unit block diagram
32-bit (write access)
4.3 CRC functional description
AHB bus
Data register (output)
The CRC calculation unit mainly consists of a single 32-bit data register, which:
● is used as an input register to enter new data in the CRC calculator (when writing into
the register)
● holds the result of the previous CRC calculation (when reading the register)
87/1416 Doc ID 018909 Rev 3
32-bit (read access)
CRC computation (polynomial: 0x4C11DB7)
Data register (input)
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