How to configure EUSART in PIC18F4550 Microcontroller

 

PIC18F4550 has an inbuilt EUSART (Enhanced USART). Normally USART can be configured as asynchronous full-duplex communication or synchronous half-duplex communication. EUSART provides additional capabilities as compared to USART, like Automatic Baud-rate Detection. Automatic baud-rate detection means that during reception there is no need to set the baud rate at controller’s side, EUSART sets it on its own which is certainly an advantage over USART. Baud rate and its calculation have been explained later in this article.

 

To use the EUSART of PIC18f4550 microcontroller following registers need to be configured.

 

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
CSRC	TX9	TXEN	SYNC	SENDB	BRGH	TRMT	TX9D

 

 

TRMT: This is a read only bit which shows the status of Shift register where data is stored.

            1 = Transmit Shift Register Empty

            0 = Transmit Shift Register Full

 

BRGH: This bit is configured to decide the speed of Asynchronous serial communication.

            1 = High speed

0 = Low speed

 

SYNC: The mode of communication is selected by this bit.

            1 = Synchronous mode

0 = Asynchronous mode

 

TXEN: This bit is set to high to enable the transmission.

 

TX9:    This bit is set to high while sending 9-bit long data.

            1 = Selects 9-bit transmission

0 = Selects 8-bit transmission

 

2. RCSTA (Receive Status and Control Register)

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
SPEN	RX9	SREN	CREN	ADDEN	FERR	OERR	RX9D

 

Fig. 5: Bit configuration of RCSTA /Receive Status and Control Register in EUSART of PIC Microcontroller

 

CREN: This bit is set to high for continuous reception enable. To stop reception the bit is set to zero.

 

RX9:   This bit is used when 9-bit long data is to be received.

            1 = Selects 9-bit reception

0 = Selects 8-bit reception

 

SPEN: This bit is used to enable/disable the serial port. (Tx and Rx pins)

            1 = Serial port enabled

0 = Serial port disabled

 

The data to be transmitted is stored in TXREG register.

 

The data to be received is stored in RCREG register.

 

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
SPPIF	ADIF	RCIF	TXIF	SSPIF	CCP1IF	TMR2IF	TMR1IF

Fig. 6: Bit Configuration of PIR1 /Peripheral Interrupt Request Register of PIC’s EUSART

 

 TXIF: This is transmitter interrupt flag bit. It becomes high when the TXREG register is empty. 

RCIF: This is receiver interrupt flag bit. It becomes high when the RCREG register is full.

 

 

Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0
SPPIE	ADIE	RCIE	TXIE	SSPIE	CCP1IE	TMR2IE	TMR1IE

Fig. 7: Bit configuration of PIE1/ Peripheral Interrupt Enable Register 1of EUSART in PIC Microcontroller

TXIE: This bit is set to high to enable the transmission interrupt.

RCIE: This bit is set to high to enable the reception interrupt.

 

 

7. BAUDCON (Baud Rate Control Register)

This register controls the baud rate and some special functionalities of serial communication like auto-baud rate detection, inversion of receiving data etc.

 

 

BRG16: This bit is used to enable/disable 16-bit baud rate register.

             1 = 16-bit Baud Rate Generator (BRG) – SPBRGH and SPBRG

 0 = 8-bit Baud Rate Generator (BRG) – SPBRG only

 

This means if the BRG16 bit is set to high, the baud rate is decided by both SPBRGH and SPBRG registers; and if it is set to low, only SPBRG register will set the baud rate.

 

These registers are used to set baud rate for the serial communication. The two registers SPBRG & SPBRGH store lower byte and higher byte respectively.

 

 

The baud rate is the speed of data in serial communication. It is also known as bits per second (bps). PIC’s EUSART provides different communication modes like asynchronous, synchronous, high-speed and low speed etc. The baud rate for different EUSART modes can be decided by different formulae. The following table shows the baud-rate formulae for different EUSART communication modes.

 

 

 

Here    :           x          = Doesn’t matter

                         Fosc   = Crystal frequency

                         n          = Value of SPBRGH : SPBRG Register pair

 

For example, if a Baud rate of 9600 is to be set for a 12MHz crystal and the mode is 8-bit, Asynchronous, then,

 

SYNC=0, BRG16=0 and BRGH=0 and the baud rate can be calculated, by using the following formula, as given below.

Project Source Code

###

// Program to depict the configuration of EUSART in PIC18F4550
// This code receives and then transmits the same data back to the PC .. // ..through PC’s Serial Port

// Configuration bits
/* _CPUDIV_OSC1_PLL2_1L, // Divide clock by 2
_FOSC_HS_1H, // Select High Speed (HS) oscillator
_WDT_OFF_2H, // Watchdog Timer off
MCLRE_ON_3H // Master Clear on
*/

void tx_data(unsigned char);

unsigned char rx_data(void);
unsigned char serial_data;
unsigned int i=0;

#define FREQ 12000000 // Frequency = 12MHz
#define baud 9600
#define spbrg_value (((FREQ/64)/baud)-1) // Refer to the formula for Baud rate calculation in Description tab

void main()
{
SPBRG=spbrg_value; // Fill the SPBRG register to set the Baud Rate
RCSTA.SPEN=1; // To activate Serial port (TX and RX pins)
TXSTA.TXEN=1; // To enable transmission
RCSTA.CREN=1; // To enable continuous reception
while(1)
{
serial_data=rx_data(); // Receive data from PC
tx_data(serial_data); // Transmit the same data back to PC
}

}

void tx_data(unsigned char data1)
{
TXREG=data1; // Store data in Transmit register
while(PIR1.TXIF==0); // Wait until TXIF gets low
}

unsigned char rx_data(void)
{
while(PIR1.RCIF==0); // Wait until RCIF gets low
return RCREG; // Retrieve data from reception register
}

###

Circuit Diagrams

Project Components

Project Video