UART Framing Mismatch – Simple Explanation

Problem

In UART communication, the first character is received correctly, but the remaining characters appear as garbage.

Root Cause

This usually happens when:

• Data bits mismatch (7 vs 8)
• Stop bits mismatch (1 vs 2)
• Baud rate mismatch
• Parity mismatch (If we select ODD and if the data has even number of one's data is not displayed because of parity mismatch)

Why First Character Looks Correct

UART resynchronizes using the START bit. The first frame may align correctly, but framing mismatch causes misalignment for following characters.

Key Lesson

UART transmitter and receiver must match exactly in:

• Baud rate ->If baudrate is mismatched we get total garbage value...Timing or sampling error
• Data bits ->If databits are mismatched first charcter will be correct,after that everything is garbage
• Parity ->when parity doesn't match no data will be displayed on the terminal...Parity Error
• Stop bits ->when stopbit is mismatced commonly we get @ or we get garbage ,sometimes we get firstcharacter correct then garbage data...This gives Framing error/

#CODE #include <lpc213x.h>

void UART0_Init(void) { PINSEL0 |= 0x05; // P0.0 = TXD0, P0.1 = RXD0 VPBDIV=0x01; U0LCR = 0x83; // 8-bit, no parity, 1 stop, DLAB = 1 U0DLL = 78; // 9600 baud @ 12MHz U0DLM = 0x00; U0LCR = 0x03; // DLAB = 0 }

void UART0_Tx(char ch) { while(!(U0LSR & (1 << 5))); // wait until THR empty U0THR = ch;

}

int main(void) { UART0_Init(); UART0_Tx('H'); UART0_Tx('i'); UART0_Tx('\n'); while(1);
}