UART Receiving keyboard input doesn't work - arduino

Question

I am having trouble with reading data sent from my laptop to the microcontroller via UART. The transmitting part works fine - I can send data to my laptop without problems, but echoing data, or reading keyboard input data from the laptop doesn't work. I have tried to implement reading both with polling and with Rx interrupt routines, but without success. The microcontroller I am using is ATMEGA2560, and I am conntected to my laptop via FTD1232 USB to TTL serial converter.
I am using Putty as a serial comm terminal, and the Arduino IDE for programming.
I am assuming that the problem is not in the hardware based on the following - I have tried initializing different USARTs and tried to use different COM ports, as well as another USB to TTL converter, various wires, but the result is the same. I have also connected another power source to supply enough voltage to all devices.
I am trying to get at least a response by turning a LED on when Rx interrupt occurs (when I type something in the terminal).
~
#define F_CPU 16000000UL //16MHz
#define BAUD 115200UL //bps
#define BAUD_PRESCALER (((F_CPU/(BAUD*8UL)))-1) //Table 101, page 212
volatile uint8_t temp;
void UART_init(){
//Set baud rate
UBRR0H = (uint8_t)(BAUD_PRESCALER >> 8); //Higher portion of the baud rate
UBRR0L = (uint8_t)BAUD_PRESCALER; //Lower portion of the baud rate
//Enable Receiver and Transmitter
UCSR0B = (1 << RXEN0) | (1 << TXEN0);
//Set frame format: 8-bit format, 1 stop bit, no parity
UCSR0C |= (3 << UCSZ00);
UCSR0C &= ~(1 << USBS0); //clear for 1 stop bit
//Set Double Speed Asynchronous mode
UCSR0A |= (1 << U2X0);
UCSR0B |= (1 << RXCIE0); //Enables interrupt rxc
}
uint8_t UART_getchar(){
//Wait for RXC flag
while(!(UCSR0A & (1 << RXC0))){};
return UDR0;
}
//Arduino setup()
void setup(){
pinMode(8, OUTPUT);
UART_init();
sei();
}
//Arduino loop()
void loop(){
delay(500);
UART_putchar('a');
}
ISR(USART0_RX_vect){
temp = UDR0;
digitalWrite(8, HIGH);
}
It is a lenghty post, but I tried to be specific and also post the whole code. The datasheet I am using for the ATMEGA2560 can be found here.
My Putty settings:
COM Port Settings

Answer 1

I've just tested it on my Mega board and it's working fine without interrupts enabled (simple loopback):
#define BAUD 115200UL
#define BAUD_PRESCALER (((F_CPU/(BAUD*8UL)))-1)
volatile uint8_t temp;
void UART_init(){
//Set baud rate
UBRR0H = (uint8_t)(BAUD_PRESCALER >> 8); //Higher portion of the baud rate
UBRR0L = (uint8_t)BAUD_PRESCALER; //Lower portion of the baud rate
//Enable Receiver and Transmitter
UCSR0B = (1 << RXEN0) | (1 << TXEN0);
//Set frame format: 8-bit format, 1 stop bit, no parity
UCSR0C |= (3 << UCSZ00);
UCSR0C &= ~(1 << USBS0); //clear for 1 stop bit
//Set Double Speed Asynchronous mode
UCSR0A |= (1 << U2X0);
// UCSR0B |= (1 << RXCIE0); //Enables interrupt rxc
}
uint8_t UART_getchar(){
//Wait for RXC flag
while(!(UCSR0A & (1 << RXC0))){};
return UDR0;
}
void UART_putchar(uint8_t data){
//Do nothing until UDR is ready
while(!(UCSR0A &(1 << UDRE0))){};
UDR0 = data;
}
void UART_putstring(uint8_t *data){
while(*data != 0x00){
UART_putchar(*data);
data++;
}
}
//Arduino setup()
void setup(){
pinMode(8, OUTPUT);
UART_init();
sei();
}
//Arduino loop()
void loop(){
UART_putchar(UART_getchar());
}
/*ISR(USART0_RX_vect){
temp = UDR0;
digitalWrite(8, HIGH);
}*/
RX interrupt must be disabled, otherwise Serial interrupt vector is taking place and polled get char can't work as characters are readed by ISR