I'm trying to code a simple program that display string I enter at pc terminal on LCD.

e.g. Mom, I love you.

But, how to know data has finished received from UART so it can be displayed at LCD?

Hi oshjdf, one method is to put a EOL character at the end of the line:

So you might have Mom, I love you.~

You could actually use the period instead of the tilde.

Or you could do a character count every sixteen characters send to LCD.

Ralph

oshjdf -

One of the more reliable ways of doing UART reads is with interrupts. Whenever a character is ready on the receive line (RX) an interrupt can be set up to simply read the character and copy it to a data array or buffer. Then the main part of the program can just sit around and wait for a change in the buffer and output the character to the LCD one at a time. When the data from the PC stops, the main program just sits and waits again after outputting to the LCD. Here is a simple interrupt code segment:

ISR(USART_RX_vect){ // this is the symbol from AVR compiler docs (interrupt.h)

//  UDR0 is data register for uart - must read it during interrupt
//  See page 185 of datasheet for chip
//  Simply read uart rx reg and copy to buffer, update pointer

    rx_buf[rx_in_idx] = UDR0;
    rx_in_idx++;
    if (rx_in_idx >= MAX_RX) rx_in_idx = 0; //wrap around to 0 if needed
    return;
}

In the main part of the code I have another buffer pointer or index variable "rx_out_idx" that I test against "rx_in_idx".

while (rx_out_idx != rx_in_idx){    // chase the input pointer
    ch = rx_buf[rx_out_idx];
    lcd_write_data(ch);
    rx_out_idx++;
    if (rx_out_idx >= MAX_RX) rx_out_idx = 0;  //wrap around to 0 if needed
}

You have to do some setup for the interrupt and the global variables, but that's not hard.