LPC1768 QEI Max Capture speed

[hdhedhu10]

QEI configuration code is shown below :

CLKPWR_ConfigPPWR (CLKPWR_PCONP_PCQEI, ENABLE);

/* As default, peripheral clock for QEI module

* is set to FCCLK / 2 */

// printf("\n qei_start");

CLKPWR_SetPCLKDiv(CLKPWR_PCLKSEL_QEI, CLKPWR_PCLKSEL_CCLK_DIV_1);

// Reset all remaining value in QEI peripheral

QEIx->QEICON = QEI_CON_RESP | QEI_CON_RESV | QEI_CON_RESI;

QEIx->QEIMAXPOS = 0x00;

QEIx->CMPOS0 = 0x00;

QEIx->CMPOS1 = 0x00;

QEIx->CMPOS2 = 0x00;

QEIx->INXCMP = 0x00;

QEIx->QEILOAD = 0x00;

QEIx->VELCOMP = 0x00;

QEIx->FILTER = 0x00;

// Disable all Interrupt

QEIx->QEIIEC = QEI_IECLR_BITMASK;

// Clear all Interrupt pending

QEIx->QEICLR = QEI_INTCLR_BITMASK;

// Set QEI configuration value corresponding to its setting up value

QEIx->QEICONF = ((QEI_CFGOPT_Type *)QEI_ConfigStruct)->ulQEIConfig;

This configuration does not seem to work if we move encoder really fast...This code is setup to use 100MHZ as peripheral clock but it still fails to recognize the signals properly when we move it fast. In slow motion it captures all the count properly.

LPC datasheet does not mention till what frequency QEI is capable of counting pulse. I have attached the logic analyzer capture of the signals which is troubling me.

[xiangjun_rong]

Hi,

I have checked the data sheet of LPC176x, but it does not list the max speed of QEI.

For your case, what is PhaseA/PhaseB signal frequency which are from encoder?

BR

XiangJun Rong

[hdhedhu10]

Maximum frequency is 350Khz.

[xiangjun_rong]

Hi,

I suppose that it is okay for the QEI counter counts both falling/rising edge of both phaseA/PhaseB signal(x4) even if the phaseA signal frequency is 350K.

Hope it can help you

BR

XiangJun Rong