AN2945

Software library

Doc ID 15468

15/18

Once you have understood the above operating principle and file organization, for simple

applications, you could virtually switch from one product to the other without referring to the

reference manual.

Let us take a practical example: an SPI peripheral configured in master mode, used to read

from/write to an external EEPROM.

Figure 4 and Figure 5 below show the initialization code (using the software library) for an

STM8S and an STM32 product, respectively.

Figure 4.

STM8S code example

Figure 5.

STM32 code example

All parameters are identical, and the procedure is similar with two function calls for both

configuration and startup. The main difference lies in the way the parameters are passed

into the function. STM32 devices use a structure passed by address whereas, for STM8S

devices, parameters are passed directly to minimize the amount of RAM needed during the

initialization phase (this is necessary with devices with down to 1 Kbyte of RAM).

Another difference is the possibility, when using STM32 devices, of specifying the data size

(8- or 16-bit) for the SPI. In the above example (Figure 5), the data size is explicitly defined,

however, the library is done so that it can be omitted: if this field is not initialized in the

structure, the 8-bit data size is used by default to maintain compatibility with STM8S

devices.

/* --------------- Initialize SPI in Master mode -------------- */

SPI_Init(SPI_FIRSTBIT_MSB,

SPI_BAUDRATEPRESCALER_4,

SPI_MODE_MASTER,

SPI_CLOCKPOLARITY_LOW,

SPI_CLOCKPHASE_2EDGE,

SPI_DATADIRECTION_1LINE_TX,

SPI_NSS_SOFT,

0x07); /* CRC Polynomial */

/* ------------------------- Enable SPI ----------------------- */

SPI_Cmd(ENABLE);

/* ---------------------- SPI1 Master ------------------------- */

SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;

SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_4;

SPI_InitStructure.SPI_Mode = SPI_Mode_Master;

SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;

SPI_InitStructure.SPI_CPHA = SPI_CPHA_2Edge;

SPI_InitStructure.SPI_Direction = SPI_Direction_1Line_Tx;

SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;

SPI_InitStructure.SPI_CRCPolynomial = 7;

SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;

SPI_Init(SPI1, &SPI_InitStructure);

/* ----------------------- Enable SPI1 ------------------------ */

SPI_Cmd(SPI1, ENABLE);

/* Private variables --------------------------------------- */

SPI_InitTypeDef SPI_InitStructure;