Serial Communication using ARM Cortex

Serial Communication:

BASICS OF SERIAL COMMUNICATION:

·        serial communication uses single data line making it much cheaper
·        enables two computers in different cities to communicate over the telephone
·        byte of data must be converted to serial bits using a parallel-in-serial-out shift register and transmitted over a single data line
·        receiving end there must be a serial-in-parallel-out shift register
·        if transferred on the telephone line, it must be converted to audio tones by modem
·        for short distance the signal can be transferred using wire
·        how PC keyboards transfer data to the motherboard
·        2 methods, asynchronous and synchronous
·        synchronous method transfers a block of data (characters) at a time
·        asynchronous method transfers a single byte at a time
·        Uses special IC chips called UART (universal asynchronous receiver-transmitter) and USART (universal synchronous asynchronous receiver-transmitter)

·        Half- and full-duplex transmission
·        if the data can be transmitted and received, it is a duplex transmission
·        simplex transmissions the computer only sends data
·        duplex transmissions can be half or full duplex
·        depends on whether or not the data transfer can be simultaneous
·        If one way at a time, it is half duplex
·        If can go both ways at the same time, it is full duplex
·        full duplex requires two wire conductors for the data lines (in addition to the signal ground)
   Asynchronous serial communication and data framing
·        data coming in 0s and 1s
·        to make sense of the data sender and receiver agree on a set of rules
·        Protocol
·        how the data is packed
·        how many bits/character
·        when the data begins and ends
·        Start and stop bits
·        asynchronous method, each character is placed between start and stop bits
·        called framing
·        start bit is always one bit
·        stop bit can be one or two bits
·        start bit is always a 0 (low)
·        stop bit(s) is 1 (high)
·        LSB is sent out first

·        in modern PCs one stop bit is standard

·        when transferring a text file of ASCII characters using 1 stop bit there is total of 10 bits for each character

·        8 bits for the ASCII code (1 parity bit), 1 bit each for the start and stop bits

·        for each 8-bit character there are an extra 2 bits, which gives 20% overhead

  Data transfer rate

·        rate of data transfer bps (bits per second)

·        widely used terminology for bps is baud rate

·        baud and bps rates are not necessarily equal

·        baud rate is defined as the number of signal changes per second

  RS232 standards

·        most widely used serial I/O interfacing standard

·        input and output voltage levels are not TTL compatible

·        1 bit is represented by -3 to -25 V

·        0 bit is +3 to +25 V

·        -3 to +3 is undefined

·        to connect RS232 to a microcontroller system must use voltage converters such as MAX232 to convert the TTL logic levels to the RS232 voltage levels, and vice versa

·        MAX232 IC chips are commonly referred to as line drivers

·       

Data communication classification

·        DTE (data terminal equipment)

·        DCE (data communication equipment)

·        DTE - terminals and computers that send and receive data

·        DCE - communication equipment responsible for transferring the data

·        simplest connection between a PC and microcontroller requires a minimum of three pins, TxD, RxD, and ground

·        Examining RS232 hand­shaking signals

·        many of the pins of the RS-232 connector are used for handshaking signals

·        they are not supported by the 8051 UART chip

·        PC/compatible COM ports

·        PC/compatible computers (Pentium) microprocessors normally have two COM ports

·        both ports have RS232-type connectors

·        COM ports are designated as COM 1 and COM 2 (replaced by USB ports)

·        can connect the AVR serial port to the COM 2 port

LPC21 CONNECTION TO RS232:

·        RxD and TxD pins in the ARM Cortex

·        LPC2148 has two pins used for transferring and receiving data serially

·        TxD and RxD are part of the port 3 group

·        these pins are TTL compatible

·        require a line driver to make them RS232 compatible

·        driver is the MAX232 chip

·        MAX232

·        converts from RS232 voltage levels to TTL voltage levels

·        uses a +5 V power source

·        MAX232 has two sets of line drivers for transferring and receiving data

·        line drivers used for TxD are called T1 and T2

·        line drivers for RxD are designated as R1 and R2

·        T1 and R1 are used together for TxD and RxD of the AVR

·        second set is left unused

·        MAX233

·        MAX233 performs the same job as the MAX232

·        eliminates the need for capacitors

·        much more expensive than the MAX232

ARM CORTEX SERIAL PORT PROGRAMMING IN C:

 
Ex1(a):
Write a program to transfer letter  "GOD BLESS YOU " serially at 9600 baud, continuously.
// Smpl_UART0 : while loop for UART0-TX keep transmitting 8 bytes string
//            : IRQ routine for UART0-RX keep receiving 8 bytes string & print to LCD
//            : need two learning board to perform UART communication (TX & RX at the same time)
//
// Nu-LB-NUC140
// pin32 GPB0/RX0 to another board's UART TX
// pin33 GPB1/TX0 to another board's UART RX

#include "NUC1xx.h"
#include "GPIO.h"
#include "SYS.h"
#include "UART.h"
void txstring(uint8_t *str)
{
    while(*str)
    {
        DrvUART_Write(UART_PORT0,str,1);
        DrvSYS_Delay(100000);
        str++;
    }
}
int main()
{
    STR_UART_T myuart;

    DrvGPIO_InitFunction(E_FUNC_UART0);       
    DrvGPIO_Open(E_GPC,12,E_IO_OUTPUT);
    DrvGPIO_Open(E_GPC,13,E_IO_OUTPUT);
    DrvGPIO_SetBit(E_GPC,12);
    DrvGPIO_SetBit(E_GPC,13);
    /* UART Setting */
    myuart.u32BaudRate         = 9600;
     myuart.u8cDataBits         = DRVUART_DATABITS_8;
    myuart.u8cStopBits         = DRVUART_STOPBITS_1;
    myuart.u8cParity         = DRVUART_PARITY_NONE;
    myuart.u8cRxTriggerLevel= DRVUART_FIFO_1BYTES;

    /* Set UART Configuration */
     if(DrvUART_Open(UART_PORT0,&myuart) != E_SUCCESS)
DrvGPIO_ClrBit(E_GPC,12);
while(1)   
    {
        txstring("GOD BLESS YOU");
    }
}

Ex2:     
Program the AVR to receive bytes of data serially and put them on LCD. Set the baud rate at 9600, 8-bit data, and 1 stop bit. 
 //
// Smpl_UART0 : while loop for UART0-TX keep transmitting 8 bytes string
//            : IRQ routine for UART0-RX keep receiving 8 bytes string & print to LCD
//            : need two learning board to perform UART communication (TX & RX at the same time)
//
// Nu-LB-NUC140
// pin32 GPB0/RX0 to another board's UART TX
// pin33 GPB1/TX0 to another board's UART RX


#include "NUC1xx.h"
#include "GPIO.h"
#include "SYS.h"
#include "UART.h"
void txstring(uint8_t *str)
{
    while(*str)
    {
        DrvUART_Write(UART_PORT0,str,1);
        DrvSYS_Delay(100000);
        str++;
    }
}



int main()
{
    uint8_t ch;
//unsigned char ch;
    STR_UART_T myuart;

    DrvGPIO_InitFunction(E_FUNC_UART0);      
    DrvGPIO_Open(E_GPC,12,E_IO_OUTPUT);
    DrvGPIO_Open(E_GPC,13,E_IO_OUTPUT);
    DrvGPIO_SetBit(E_GPC,12);
    DrvGPIO_SetBit(E_GPC,13);
    /* UART Setting */
    myuart.u32BaudRate         = 9600;
     myuart.u8cDataBits         = DRVUART_DATABITS_8;
    myuart.u8cStopBits         = DRVUART_STOPBITS_1;
    myuart.u8cParity         = DRVUART_PARITY_NONE;
    myuart.u8cRxTriggerLevel= DRVUART_FIFO_1BYTES;

    /* Set UART Configuration */
     if(DrvUART_Open(UART_PORT0,&myuart) != E_SUCCESS)
DrvGPIO_ClrBit(E_GPC,12);
while(1)  
    {
        txstring("waiting of data");
        //txstring("\n\n");
        while(DrvUART_Read(UART_PORT0,&ch,1)!=E_SUCCESS);
        DrvSYS_Delay(100000);
        DrvUART_Write(UART_PORT0,&ch,1);
      
        //DrvUART_Write(UART_PORT0,&ch,1);
        txstring(&ch);
    }
}