Comparator on FRDM-MCXN947

[John_Adams]

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

[Harry_Zhang]

Hi @John_Adams 

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

BR

Harry

[John_Adams]

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

[Harry_Zhang]

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.

BR

Harry

[John_Adams]

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