ST STM32F31xx User Manual

STM32F30xx Standard Peripheral Library
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Peripheral registers bits
All the peripheral registers bits are defined as constants in the stm32f30x.h file. They are
defined as acronyms written in upper-case into the form:
PPP_<register_name>_<bit_name>
Example:
#define SPI_CR1_CPHA ((uint16_t)0x0001) /*!< Clock Phase */
#define SPI_CR1_CPOL ((uint16_t)0x0002) /*!< Clock Polarity */
#define SPI_CR1_MSTR ((uint16_t)0x0004) /*!< Master Selection */
#define SPI_CR1_BR ((uint16_t)0x0038) /*!< BR[2:0] bits (Baud
Rate Control) */
#define SPI_CR1_BR_0 ((uint16_t)0x0008) /*!< Bit 0 */
#define SPI_CR1_BR_1 ((uint16_t)0x0010) /*!< Bit 1 */
#define SPI_CR1_BR_2 ((uint16_t)0x0020) /*!< Bit 2 */
1.1.4 Bit-Banding
The Cortex-M4 memory map includes two bit-band memory regions. These regions map
each word in an alias region of memory to a bit in a bit-band region of memory. Writing to a
word in the alias region has the same effect as a read/modify/write operation on the
targeted bit in the bit-band region.
All the STM32F30/F31xx peripheral registers are mapped in a bit-band region. This feature
is consequently intensively used functions performing single bit set/reset in order to reduce
and optimize code size.
The sections below describe how the bit-band access is used in the Library.
Mapping formula
The mapping formula shows how to link each word in the alias region to a corresponding
target bit in the bit-band region. The mapping formula is given below:
bit_word_offset = (byte_offset x 32) + (bit_number × 4)
bit_word_addr = bit_band_base + bit_word_offset
where:
 bit_word_offset is the position of the target bit in the bit-band memory region
 bit_word_addr is the address of the word in the alias memory region that maps to the
targeted bit.
 bit_band_base is the starting address of the alias region
 byte_offset is the number of the byte in the bit-band region that contains the targeted
bit
 bit_number is the bit position (0-7) of the targeted bit.
Example of implementation
The following example shows how to map the PLLON[24] bit of RCC_CR register in the
alias region:
...
/*!< Peripheral base address in the alias region */
#define PERIPH_BASE ((uint32_t)0x40000000)
...
/*!< Peripheral base address in the bit-band region */
#define PERIPH_BB_BASE ((uint32_t)0x42000000)
...

ST STM32F31xx Specifications

General

Brand	ST
Model	STM32F31xx
Category	Microcontrollers
Language	English