Hallo,
auf einem STM32F103 High Density Board ohne externen Quarz möchte ich
eine PWM mit 15kHz generieren. Es geht zwar aber, seltsamerweise beträgt
die PWM Frequenz am Oszi immer die Hälfte meiner berechneten Frequenz.
Systemtakt Einstellung auf 48MHz.
1 | RCC_PLLConfig(RCC_PLLSource_HSI_Div2, RCC_PLLMul_12); // 48MHz
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2 | RCC_PLLCmd(ENABLE);
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3 |
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4 | while (RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET) {
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5 | }
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6 | RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);
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7 |
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8 | /* Set HCLK, PCLK1, and PCLK2 to SCLK (these are default */
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9 | RCC_HCLKConfig(RCC_SYSCLK_Div1); // 48 MHz
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10 | RCC_PCLK1Config(RCC_HCLK_Div2); // APB1 24MHz, max 36MHz
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11 | RCC_PCLK2Config(RCC_HCLK_Div1); // APB2 48MHz
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danach die gesetzten Werte geprüft
1 | trace_printf("SYSCLK_Frequency: %u \n", clocks.SYSCLK_Frequency);
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2 | trace_printf("PCLK1_Frequency: %u \n", clocks.PCLK1_Frequency);
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3 | trace_printf("PCLK2_Frequency: %u \n", clocks.PCLK2_Frequency);
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4 | trace_printf("ADCCLK_Frequency: %u \n", clocks.ADCCLK_Frequency);
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5 |
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6 | SYSCLK_Frequency: 48000000
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7 | PCLK1_Frequency: 24000000
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8 | PCLK2_Frequency: 48000000
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9 | ADCCLK_Frequency: 24000000
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mit dieser PWM Initialisierung beträgt die PWM Frequenz 15kHz wie
gewünscht. Wenn ich die Werte in der Formel einsetze, kommt 30kHz raus.
Beträgt der APB2 Takt etwa 24MHz?
1 | /* TIM1 clock enable APB2 = 48MHz */
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2 | /* 15kHz PWM_fr = TIM_CLK_fr / (Prescaler + 1) / (Period + 1) TIM_CLK_fr = 48MHz */
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3 |
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4 | /* TIM1 clock enable APB2 = 48MHz */
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5 | RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);
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6 |
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7 | TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
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8 | TIM_OCInitTypeDef TIM_OCInitStructure;
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9 |
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10 | /* Initialize basic structures to default */
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11 | TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
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12 | TIM_OCStructInit(&TIM_OCInitStructure);
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13 |
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14 | TIM_TimeBaseStructure.TIM_Prescaler = 0;
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15 | TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_CenterAligned1;
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16 | TIM_TimeBaseStructure.TIM_Period = 1600 - 1;
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17 | TIM_TimeBaseStructure.TIM_ClockDivision = 0;
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18 | TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
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19 |
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20 | TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
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