Comparator on FRDM-MCXN947

John_Adams — Thu, 20 Mar 2025 20:22:11 GMT

Hi,

I would like to use a comparator in my project on FRDM-MCXN947, I want to trigger an interrupt in case the voltage at its input reaches 4.6V.

Is it possible to use the comparator on the FRDM-MCXN947 board in this way? If so, how is it necessary to set up the VREF, DAC and CMP modules in this case?

John Adams

Re: Comparator on FRDM-MCXN947

John_Adams — Fri, 21 Mar 2025 15:14:36 GMT

More likely,

how do I enable CMP on P0_22 (CMP1_IN2).

/* Configure LPCMP input channels. */ LPCMP_SetInputChannels(CMP1, 2, 7);

This is probably not correct, isn't it?

Thank you

Re: Comparator on FRDM-MCXN947

Harry_Zhang — Mon, 24 Mar 2025 03:44:02 GMT

Hi @John_Adams

Based on your needs, i think you can refer to the lpcmp_interrupt demo in SDK.

Harry

Re: Comparator on FRDM-MCXN947

John_Adams — Mon, 24 Mar 2025 14:21:53 GMT

Hi Harry,

I have already done that, I tried to run the demo with the original pin P1_0 (CMP0_IN0) and everything worked (i.e. the comparator reacted to changes in input voltage), but then I tried to change the pin on P0_22 where the channel CMP1_IN2 is output and adjusted the SW accordingly:

const port_pin_config_t port0_22_pin_config = {/* Internal pull-up/down resistor is disabled */ kPORT_PullDisable, /* Low internal pull resistor value is selected. */ kPORT_LowPullResistor, /* Fast slew rate is configured */ kPORT_FastSlewRate, /* Passive input filter is disabled */ kPORT_PassiveFilterDisable, /* Open drain output is disabled */ kPORT_OpenDrainDisable, /* Low drive strength is configured */ kPORT_LowDriveStrength, /* Pin is configured as CMP1_IN1 */ kPORT_MuxAlt0, /* Digital input disabled; it is required for analog functions */ kPORT_InputBufferDisable, /* Digital input is not inverted */ kPORT_InputNormal, /* Pin Control Register fields [15:0] are not locked */ kPORT_UnlockRegister}; /* PORT0_22 is configured as CMP1_IN2 */ PORT_SetPinConfig(PORT0, 22U, &port0_22_pin_config);

And also changed the demo app accordingly, but CMP is not reacting:

#include "fsl_debug_console.h" #include "pin_mux.h" #include "clock_config.h" #include "board.h" #include "fsl_lpcmp.h" #include "fsl_vref.h" #include "fsl_spc.h" /******************************************************************************* * Definitions ******************************************************************************/ #define DEMO_LPCMP_BASE CMP1 #define DEMO_LPCMP_USER_CHANNEL 1U #define DEMO_LPCMP_DAC_CHANNEL 7U #define DEMO_LPCMP_IRQ HSCMP1_IRQn #define LED_INIT() LED_RED_INIT(LOGIC_LED_ON) #define LED_ON() LED_RED_ON() #define LED_OFF() LED_RED_OFF() #define DEMO_LPCMP_IRQ_HANDLER_FUNC HSCMP1_IRQHandler #define DEMO_VREF_BASE VREF0 #define DEMO_SPC_BASE SPC0 /******************************************************************************* * Prototypes ******************************************************************************/ /******************************************************************************* * Variables ******************************************************************************/ /******************************************************************************* * Code ******************************************************************************/ /*! * @brief Main function */ int main(void) { lpcmp_config_t mLpcmpConfigStruct; lpcmp_dac_config_t mLpcmpDacConfigStruct; /* Initialize hardware. */ vref_config_t vrefConfig; /* attach FRO 12M to FLEXCOMM4 (debug console) */ CLOCK_SetClkDiv(kCLOCK_DivFlexcom4Clk, 1U); CLOCK_AttachClk(BOARD_DEBUG_UART_CLK_ATTACH); /* attach FRO 12M to CMP1 */ CLOCK_SetClkDiv(kCLOCK_DivCmp1FClk, 1U); CLOCK_AttachClk(kFRO12M_to_CMP1F); /* enable CMP1, CMP1_DAC and VREF. */ SPC_EnableActiveModeAnalogModules(SPC0, kSPC_controlAllModules); VREF_GetDefaultConfig(&vrefConfig); /* Initialize the VREF mode. */ VREF_Init(VREF0, &vrefConfig); /* Get a 1.8V reference voltage. */ VREF_SetTrim21Val(VREF0, 8U); BOARD_InitPins(); BOARD_InitBootClocks(); BOARD_InitDebugConsole(); PRINTF("LPCMP Interrupt Example.\r\n"); /* * k_LpcmpConfigStruct->enableStopMode = false; * k_LpcmpConfigStruct->enableOutputPin = false; * k_LpcmpConfigStruct->useUnfilteredOutput = false; * k_LpcmpConfigStruct->enableInvertOutput = false; * k_LpcmpConfigStruct->hysteresisMode = kLPCMP_HysteresisLevel0; * k_LpcmpConfigStruct->powerMode = kLPCMP_LowSpeedPowerMode; * k_LpcmpConfigStruct->functionalSourceClock = kLPCMP_FunctionalClockSource0; */ LPCMP_GetDefaultConfig(&mLpcmpConfigStruct); /* Init the LPCMP module. */ LPCMP_Init(CMP1, &mLpcmpConfigStruct); /* Configure the internal DAC to output half of reference voltage. */ mLpcmpDacConfigStruct.enableLowPowerMode = false; mLpcmpDacConfigStruct.referenceVoltageSource = kLPCMP_VrefSourceVin2; mLpcmpDacConfigStruct.DACValue = 0xFF; //((LPCMP_DCR_DAC_DATA_MASK >> LPCMP_DCR_DAC_DATA_SHIFT) >> 1U); /* Half of reference voltage. */ LPCMP_SetDACConfig(CMP1, &mLpcmpDacConfigStruct); /* Configure LPCMP input channels. */ LPCMP_SetInputChannels(CMP1, 0x02, 0x07); /* Init the LED. */ LED_INIT(); /* Enable the interrupt. */ EnableIRQ(HSCMP1_IRQn); LPCMP_EnableInterrupts(CMP1, kLPCMP_OutputRisingInterruptEnable | kLPCMP_OutputFallingInterruptEnable); while (1) { ; } }

so how come the comparator isn't responding?

Thank you,

John Adams

Re: Comparator on FRDM-MCXN947

Harry_Zhang — Mon, 31 Mar 2025 07:55:49 GMT

Hi @John_Adams

Is the voltage at P0_22 actually reaching the expected 4.6V?

If it does not work.

You can try switching to another pin that supports CMP1.

Harry

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