{"id":4023,"date":"2020-12-03T08:32:21","date_gmt":"2020-12-03T08:32:21","guid":{"rendered":"http:\/\/fastbitlab.com\/?p=4023"},"modified":"2023-09-06T11:58:46","modified_gmt":"2023-09-06T06:28:46","slug":"implementation-of-i2c-init-api-part-1","status":"publish","type":"post","link":"https:\/\/fastbitlab.com\/blog\/implementation-of-i2c-init-api-part-1\/","title":{"rendered":"STM32 I2C Lecture 14: Implementation of I2C init API: Part 1"},"content":{"rendered":"
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Implementation of I2C init API: Part 1<\/span><\/h1>\n
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In this article, let\u2019s code I2C_Init. Let\u2019s discuss the things that need to be configured in the I2C registers. <\/span><\/p>\n

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  1. To control the acking, you need to configure the ACK (10<\/span>th<\/span>  bit) bit of the CR1 register, as shown in Figure 1.<\/span><\/span><\/li>\n<\/ol>\n
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    Figure 1. Code for configuring ACK of CR1 register.<\/span><\/figcaption><\/figure>\n

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    2. Configure the FREQ field of the CR2 register. <\/span><\/p>\n

    The FREQ bits must be configured with the APB clock frequency value. That means the exact clock frequency of the APB1 bus must be calculated. We already know that in our case, it is 16. But it need not be the same always. The user may change this value. Therefore, it is required to calculate the FREQ field. <\/span><\/p>\n

    Let’s create a small function to calculate the APB1 bus clock’s value, as shown in Figure 2.<\/span><\/p>\n

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    Figure 2. Function to calculate the APB1 bus clock’s value.<\/span><\/figcaption><\/figure>\n

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    Refer to the clock tree shown in Figure 3 to know how the PCLK1 is calculated. <\/span><\/p>\n

    To calculate the PCLK1, First, find out the source by reading the RCC registers. <\/span>After that, calculate the AHB prescaler and APB1 prescaler. <\/span><\/p>\n

    The value of PCLK1 depends on the clock source, which means the system clock, and it is decided depending on the HSE, HSI, PLLCLK, PLLR, etc. In our case, the system clock is HSI (16MHz), which is then divided by the AHB prescaler to get the AHB clock.<\/span><\/p>\n

    To obtain the APB1 clock, divide the AHB clock by APB1 prescaler, and then the APB1 clock is delivered to the APB1 peripherals where I2C is connected.<\/span><\/p>\n

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    Figure 3. Clock tree<\/span><\/figcaption><\/figure>\n

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    In the clock configuration registers of RCC, refer to the bit numbers 2 and 3 (Figure 4). <\/span><\/p>\n

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    Figure 4. Bit 2 and 3 of Clock configuration registers of RCC.<\/span><\/figcaption><\/figure>\n

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    Calculate the values of bits 2 and 3 to determine which clock source is used as the system clock. Now let\u2019s write the code for finding the clock source.<\/span><\/p>\n