I have a couple of different evaluation boards but finding the pwm control difficult to understand. For example I have 6 pwm outs on a board, can I use each one individually, ie, setting different duty cycles for each one or do all the pwm outs produce the same signal?
If this is the case I guess the way round it is to write pwm code in software and use a digital out switching quickly?
Hello Julian,
as far as I know from reading the documentation of PwmOut, you can specify the frequency and duty cycle (only) for each pin individually.
Just create an instance of PwmOut for every PWM pin you need. The pin name must be provided as a parameter in the constructor.
Best Regards,
Stefan
Hello Julian,
As Stefan says, you can specify the frequency and duty cycle for each pin individually. However, PWM is controlled by hardware Timer-channels. So if several pins share the same Timer-channel then setting PwmOut frequency or duty cycle for one pin will modify them for the other pins too. For STM targets, the PWM Timer-channel combination of individual pins is defined in the PeripheralPinMaps.h file of the given target. For example, for the NUCLEO_F411RE it looks like as below (the comment at the end of each line indicates the used Timer-channel) :
...
//*** PWM ***
// TIM5 cannot be used because already used by the us_ticker
MSTD_CONSTEXPR_OBJ_11 PinMap PinMap_PWM[] = {
{PA_0, PWM_2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM2, 1, 0)}, // TIM2_CH1
// {PA_0, PWM_5, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM5, 1, 0)}, // TIM5_CH1
{PA_1, PWM_2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM2, 2, 0)}, // TIM2_CH2
// {PA_1, PWM_5, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM5, 2, 0)}, // TIM5_CH2
// {PA_2, PWM_2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM2, 3, 0)}, // TIM2_CH3 // Connected to STDIO_UART_TX
// {PA_2, PWM_5, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM5, 3, 0)}, // TIM5_CH3 // Connected to STDIO_UART_TX
// {PA_2, PWM_9, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM9, 1, 0)}, // TIM9_CH1 // Connected to STDIO_UART_TX
// {PA_3, PWM_2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM2, 4, 0)}, // TIM2_CH4 // Connected to STDIO_UART_RX
// {PA_3, PWM_5, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM5, 4, 0)}, // TIM5_CH4 // Connected to STDIO_UART_RX
// {PA_3, PWM_9, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM9, 2, 0)}, // TIM9_CH2 // Connected to STDIO_UART_RX
{PA_5, PWM_2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM2, 1, 0)}, // TIM2_CH1 // Connected to LD2 [Green Led]
{PA_6, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 1, 0)}, // TIM3_CH1
{PA_7, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 1, 1)}, // TIM1_CH1N
{PA_7_ALT0, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 2, 0)}, // TIM3_CH2
{PA_8, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 1, 0)}, // TIM1_CH1
{PA_9, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 2, 0)}, // TIM1_CH2
{PA_10, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 3, 0)}, // TIM1_CH3
{PA_11, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 4, 0)}, // TIM1_CH4
{PA_15, PWM_2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM2, 1, 0)}, // TIM2_CH1
{PB_0, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 2, 1)}, // TIM1_CH2N
{PB_0_ALT0, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 3, 0)}, // TIM3_CH3
{PB_1, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 3, 1)}, // TIM1_CH3N
{PB_1_ALT0, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 4, 0)}, // TIM3_CH4
{PB_3, PWM_2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM2, 2, 0)}, // TIM2_CH2 // Connected to SWO
{PB_4, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 1, 0)}, // TIM3_CH1
{PB_5, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 2, 0)}, // TIM3_CH2
{PB_6, PWM_4, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM4, 1, 0)}, // TIM4_CH1
{PB_7, PWM_4, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM4, 2, 0)}, // TIM4_CH2
{PB_8, PWM_4, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM4, 3, 0)}, // TIM4_CH3
{PB_8_ALT0, PWM_10, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM10, 1, 0)}, // TIM10_CH1
{PB_9, PWM_4, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM4, 4, 0)}, // TIM4_CH4
{PB_9_ALT0, PWM_11, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF3_TIM11, 1, 0)}, // TIM11_CH1
{PB_10, PWM_2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM2, 3, 0)}, // TIM2_CH3
{PB_13, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 1, 1)}, // TIM1_CH1N
{PB_14, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 2, 1)}, // TIM1_CH2N
{PB_15, PWM_1, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF1_TIM1, 3, 1)}, // TIM1_CH3N
{PC_6, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 1, 0)}, // TIM3_CH1
{PC_7, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 2, 0)}, // TIM3_CH2
{PC_8, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 3, 0)}, // TIM3_CH3
{PC_9, PWM_3, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM3, 4, 0)}, // TIM3_CH4
{NC, NC, 0}
};
...
So to have fully independent PwmOut’s you should select a combination of pins which do not share the same Timer-channel.
Best regards, Zoltan
Thanks guys, thats what i thought, guess i must have put two of the outputs using the same timer. Will have another look at what i was doing.