QDEC

QDEC Demo Code Support List

The description of QDEC demo code 1 is shown in the following table.

QDEC Demo Code 1 Description

Demo 1	qdec_demo.c
Sample Purpose	Demonstrate how QDEC works.
Brief Introduction	This sample code demonstrates how QDEC works. The chip will detect the direction and count of wheel turns.
File Path	sdk\src\sample\io_demo\qdec\qdec_demo.c
Function Entry	qdec_demo()
Hardware Connection	As shown in QDEC Demo Code 1 Hardware Connection Diagram. On EVB, connect P1_0 to the PHA of the wheel, connect P1_1 to the PHB of the wheel.
QDEC PHA Pin Definition	#define QDEC_Y_PHA_PIN P1_0
QDEC PHB Pin Definition	#define QDEC_Y_PHB_PIN P1_1
QDEC Axial	Y
Scan Clock	50KHz
Debounce Clock	5KHz
Debounce	Enable
Debounce Time	5ms
Expected Result	Press the Reset button on the EVB. When the wheel is turned, the direction is recorded in the variable dir, and the count is recorded in the variable y_axis.

The hardware connection of QDEC demo code 1 is shown in the figure below.

QDEC Demo Code 1 Hardware Connection Diagram

Functional Overview

As shown in the following figure, QDEC is used to detect the motion state of the rotation-sensing device. When the rotating device moves, it will output two quadrature signals PHA and PHB. QDEC judges the direction of rotation by detecting the phase change of PHA and PHB.

Schematic Diagram of Two Quadrature Signals of QDEC

Feature List

• Support 3 axes.

• Support hardware debounce: debounce time for each axis can be set independently.

• Support initial phase setting.

• Support illegal phase change detection.

• 16-bit phase change counter.

Note

RTL87x3E cannot disable the hardware debounce function. RTL87x3D can disable the hardware debounce function.

Direction Judgment and Counting Method

1. PHA and PHB are combined into a 2-bit number. PHA is the high bit, and PHB is the low bit.

2. The phases are divided into four types: 00, 01, 11, and 10.

3. As shown in the following figure, changes in the order of 00, 01, 11, and 10 are defined as positive. When the counter scale is set to 0, the counter will increase by one when the phase changes once. When the counter scale is set to 1, the counter will increase by one when the phase changes twice.

4. Changes in the order of 00, 10, 11, and 01 are defined as negative. When the counter scale is set to 0, the counter will decrease by one when the phase changes once. When the counter scale is set to 1, the counter will decrease by one when the phase changes twice.

5. PHA and PHB should only have one signal change at a time. If both signals change at the same time, the state is considered wrong. When this error state occurs, the counter does not count. Illegal interrupts can be turned on to detect this error condition.

Schematic Diagram of QDEC Direction Judgment

Program Examples

Operation Flow

QDEC operation flow is shown in the following figure.

QDEC Operation Flow Chart

The codes below demonstrate the QDEC operation flow.

RCC_PeriphClockCmd(APBPeriph_QDEC, APBPeriph_QDEC_CLOCK, ENABLE);

QDEC_InitTypeDef qdecInitStruct;
QDEC_StructInit(&qdecInitStruct);
qdecInitStruct.ScanClockKHZ         = 50; /*!< 50KHz */
qdecInitStruct.DebonceClockKHZ     = 5; /*!< 5KHz */
qdecInitStruct.axisConfigY       = ENABLE;
qdecInitStruct.debounceEnableY   = Debounce_Enable;
qdecInitStruct.debounceTimeY     = 5 * 5; /*!< 5ms */

QDEC_Init(QDEC, &qdecInitStruct);

RamVectorTableUpdate(Qdecode_VECTORn, (IRQ_Fun)qdec_handler);
QDEC_INTConfig(QDEC, QDEC_Y_INT_NEW_DATA, ENABLE);

NVIC_InitTypeDef nvic_init_struct;
nvic_init_struct.NVIC_IRQChannel         = QDEC_IRQn;
nvic_init_struct.NVIC_IRQChannelCmd      = (FunctionalState)ENABLE;
nvic_init_struct.NVIC_IRQChannelPriority = 3;
NVIC_Init(&nvic_init_struct);

QDEC_Cmd(QDEC, QDEC_AXIS_Y, ENABLE);

QDEC interrupt handle flow is shown in the following figure.

QDEC Interrupt Handle Flow Chart

The codes below demonstrate the QDEC interrupt handle flow.

void qdec_handler(void)
{
   /* Check Y-axis counter interrupt status flag */
   if (QDEC_GetFlagState(QDEC, QDEC_FLAG_NEW_CT_STATUS_Y) == SET)
   {
      /* Mask Y-axis counter interrupt */
      QDEC_INTMask(QDEC, QDEC_Y_CT_INT_MASK, ENABLE);

      /* Read direction */
      dir = QDEC_GetAxisDirection(QDEC, QDEC_AXIS_Y);
      /* Read counter count value */
      y_axis = QDEC_GetAxisCount(QDEC, QDEC_AXIS_Y);
      IO_PRINT_INFO2("qdec_handler: dir %d, y_axis %d", dir, y_axis);
      /* clear Y-axis counter interrupt status flag */
      QDEC_ClearFlags(QDEC, QDEC_CLR_NEW_CT_Y);
      /* Unmask Y-axis counter interrupt */
      QDEC_INTMask(QDEC, QDEC_Y_CT_INT_MASK, DISABLE);
   }
}