Robelopment

Serial Communication Using the EUSART1 Module

 

The Enhanced Universal Synchronous Asynchronous Receiver Transmitter (EUSART) module is one of two serial I/O modules. (Generically, the EUSART is also known as a Serial Communications Interface or SCI.)

 

The EUSART can be configured as a full-duplex, asynchronous system that can communicate with peripheral devices, such as CRT terminals and personal computers. It can also be configured as a half-duplex synchronous system that can communicate with peripheral devices, such as A/D or D/A integrated circuits, serial EEPROMs, etc.

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As mentioned before, the PIC45K80 is equipped with two independent EUSART modules, referred to as EUSART1 and EUSART2. They can be configured in the following modes:

• Asynchronous (full duplex) with:

  • Auto-wake-up on character reception

  • Auto-baud calibration

  • 12-bit Break character transmission

• Synchronous – Master (half duplex) with selectable clock polarity

• Synchronous – Slave (half duplex) with selectable clock polarity

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It was important to take into account that the pins of EUSART1 and EUSART2 are multiplexed with the functions with the following ports.

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The operation of each Enhanced USARTx module is controlled through three registers:

1. Transmit Status and Control (TXSTAx)

2. Receive Status and Control (RCSTAx)

3. Baud Rate Control (BAUDCONx)

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In this project, we used the USART1 with the following configuration:

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    TXSTA1=0b00100000;

    RCSTA1=0b10010000;

    BAUDCON1=0b00000000;

    SPBRG1=12;

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Since all the code was implemented using interruptions, it was necessary to set the following priorities as high:

     //Receiver priorities 

    RC1IE=1;

    RC1IP=1;

    RC1IF=0;

   

    //Transmitter priorities

    //TXBIEbits.TX1IE=1;

    PIE1bits.TX1IE=0;

    TX1IP=1;

    PIR1bits.TX1IF=0;

 

And the code within the interuption is the following:

 

void interrupt ISR_alta (void)  //high priority{

    //Transmitter

    if ((PIE1bits.TX1IE==1) && (PIR1bits.TX1IF==1)){

        PIE1bits.TX1IE = 0;

        banderaTX=1;

}

    //Receiver

    if ((RC1IE==1) && (RC1IF==1)){

        recepcion[k] = RCREG1;

        banderaRC=1;

    }

}

 

 

The other functions related to the serial communication are:

• sendMsg();

• getInstruction();

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Implementing I2C communication with the MSSP module for the MPU6050

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I2C Communication

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The Master Synchronous Serial Port (MSSP) module is a serial interface, useful for communicating with other peripheral or microcontroller devices. These peripheral devices may be devices such as serial EEPROMs, shift registers, display drivers and A/D Converters. The MSSP module can operate in either of two modes:

• Serial Peripheral Interface (SPI)

• Inter-Integrated Circuit (I2C™)

  • Full Master mode

  • Slave mode (with general address call)

The I2C interface supports the following modes in hardware:

• Master mode

• Multi-Master mode

• Slave mode with 5-bit and 7-bit address masking (with address masking for both 10-bit and 7-bit addressing)

 

The MSSP module has three associated control registers. These include a status register (SSPSTAT) and two control registers (SSPCON1 and SSPCON2). The use of these registers and their individual configuration bits differ significantly depending on whether the MSSP module is operated in SPI or I2C mode.

 

The MSSP module in I2C mode fully implements all master and slave functions (including general call support), and provides interrupts on Start and Stop bits in hardware to determine a free bus (multi-master function). The MSSP module implements the standard mode specifications, as well as 7-bit and 10-bit addressing.

 

Two pins are used for data transfer:

• Serial Clock (SCL) – RC3/REFO/SCL/SCK

• Serial Data (SDA) – RC4/SDA/SDI

 

We had to configure these pins as inputs by setting the associated TRIS bits, which in the case of the PIC18F45K80 were:

• TRISC4 = 1;

• TRISC3 = 1;

 

The MSSP module has seven registers for I2C operation. These are:

• MSSP Control Register 1 (SSPCON1)

• MSSP Control Register 2 (SSPCON2)

• MSSP Status Register (SSPSTAT)

• Serial Receive/Transmit Buffer Register (SSPBUF)

• MSSP Shift Register (SSPSR) – Not directly accessible

• MSSP Address Register (SSPADD)

• I2C Slave Address Mask Register (SSPMSK)

 

SSPCON1, SSPCON2 and SSPSTAT are the control and status registers in I2C mode operation. The SSPCON1 and SSPCON2 registers are readable and writable. The lower 6 bits of the SSPSTAT are read-only. The upper two bits of the SSPSTAT are read/write. SSPSR is the shift register used for shifting data in or out. SSPBUF is the buffer register to which data bytes are written to or read from.

 

For this project, the configuration of these mentioned registers is the following:

SSPSTATbits.SMP = 0;

SSPSTATbits.CKE = 1;

SSPCON1 = 0b00101000;

SSPCON2 =0b00000000;

SSPADD = BITRATE;

 

 For a correct implementation of the I2C communication is necessary to enable the following interruption priority levels:

SSPIE = 1;                   

SSPIF = 0;

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The functions related to the I2C communication are the following:

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void I2C_Ready();                                  // Check weather I2C is ready/idle or not
void I2C_Init();                                       //Initialize I2C configuration
char I2C_Start(char);                             //Send START pulse with slave device write address
void I2C_Start_Wait(char);    //Send START pulse with slave device write address until acknowledge
char I2C_Repeated_Start(char);       //Send REPEATED START pulse with slave device read address
char I2C_Stop();                                 //Send STOP pulse
char I2C_Write(unsigned char);          // Write data/address to slave device
void I2C_Ack();                                    //Send acknowledge to slave for continue read
void I2C_Nack();                   //Send negative acknowledge to slave for stop current communication
char I2C_Read(char);                    //Read data from slave devices with 0=Ack & 1=Nack

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Interfacing MPU6050 Accelerometer - Gyroscope

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As mentioned before, the MPU6050 generates 7 different values:

1. Acceleration along the x-axis

2. Acceleration along the y-axis

3. Acceleration along the z-axis

4. Acceleration around the x-axis

5. Acceleration around the y-axis

6. Acceleration around the z-axis

7. Temperature

The MPU6050 can communicate with the PIC18F45K80 micro controller using the previously I2C communication protocol.

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How does the gyroscope work?

When the gyros are rotated about any of the sense axes, the Coriolis Effect causes a vibration that is detected by a MEM inside MPU6050.  This voltage is digitized using 16-bit ADC to sample each axis.  The full-scale range of output are +/- 250, +/- 500, +/- 1000, +/- 2000.

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How does the accelerometer work?

Acceleration along the axes deflects the movable mass. This displacement of moving plate (mass) unbalances the differential capacitor which results in sensor output. Output amplitude is proportional to acceleration. A 16-bit ADC is used to get digitized output.  The full-scale range of acceleration are +/- 2g, +/- 4g, +/- 8g, +/- 16g.  It measured in g (gravity force) unit. When device placed on flat surface it will measure 0g on X and Y axis and +1g on Z axis

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In this project, we currently use only the accelerometer, e.g., the values 1, 2 and 3. We communicate with the PIC18 to the MPU6050 using the following functions:

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MPU6050_Init();

MPU_Start_Loc();

I2C_Stop();

readIMU();

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The MPU6050_Init() function is only used once at the beginning of the program. It is necessary for correctly initializing the MPU6050.

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The functions MPU_Start_Loc() and I2C_Stop() are used within the the readIMU() function. You can see how this functions are implemented in the following piece of code:

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