Crc Calculation Unit; Crc Introduction; Crc Main Features; Figure 3. Crc Calculation Unit Block Diagram - ST STM32F101 series Reference Manual

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CRC calculation unit

Low-density devices are STM32F101xx, STM32F102xx and STM32F103xx
microcontrollers where the Flash memory density ranges between 16 and 32 Kbytes.
Medium-density devices are STM32F101xx, STM32F102xx and STM32F103xx
microcontrollers where the Flash memory density ranges between 64 and 128 Kbytes.
High-density devices are STM32F101xx and STM32F103xx microcontrollers where the
Flash memory density ranges between 256 and 512 Kbytes.
XL-density devices are STM32F101xx and STM32F103xx microcontrollers where the
Flash memory density ranges between 768 Kbytes and 1 Mbyte.
Connectivity line devices are STM32F105xx and STM32F107xx microcontrollers.
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 link-
time and stored at a given memory location.
4.2

CRC main features

• Uses CRC-32 (Ethernet) polynomial: 0x4C11DB7
–
• 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
32 26 23 22
X + X + X + X

Figure 3. CRC calculation unit block diagram

CRC computation (polynomial: 0x4C11DB7)
32-bit (write access)
DocID13902 Rev 15
16 12 11
+ X + X + X + X
Figure 3.
AHB bus
Data register (output)
Data register (input)
CRC calculation unit
10 8 7 5 4
+X + X + X + X
32-bit (read access)
2
+ X + X +1
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