1. Error Detection/Correction Section 1.7 Section 3.9 Bonus Material: Hamming Code

2. ASCII Code

3. Format effector: control layout Communication Control Characters: frame a text message.

4. ASCII Examples ASCII A=1000001 ASCII T=1010100

5. ASCII Code 1011001 (Y) 1001110 (N) If the probability of a bit flipping event is 1%, what is the likely hood that 4 bits are flipped simultaneously?

6. Parity Bit ASCII characters are stored one per byte (8 bits) The leftmost bit is called the parity bit A parity bit is an extra bit included with a message to make the total number of 1’s either even or odd.

7. Examples of Parity Bit Even Parity – ASCII A=01000001 – ASCII T=11010100 Odd Parity – ASCII A=11000001 – ASCII T=01010100

8. Signal Transmission Algorithm (Even Parity System) A parity bit is generated and attached to the raw data An eight-bit sequence including the parity bit are sent. The parity of each character is checked at the receiving end. If the parity of the received character is not even, then at least one bit has changed value during transmission. The sender must retransmit the signal.

9. Parity Generator The circuit that generates the parity bit in the transmitter is called a parity generator. (Truth Table)

10. Parity Checker The Circuit that checks the parity in the receiver is called a parity checker.

11. Limitation of Parity Checking (1)

12. Hardware implementation Review of two-terminal XOR/XNOR Three terminal XOR/XNOR Hardware Implementation

13. Two-terminal XOR

14. Gate Level Implementation of XOR

15. Alternative Implementation of XOR

16. Parity Generator The circuit that generates the parity bit in the transmitter is called a parity generator. (Truth Table)

17. Three-Terminal XOR

18. Four-Input Odd Function

19. Parity Error Check

20. Error Correction Hamming Code Use check bits to correct error

21. Raw Data Notation: (bit 1, bit 2, bit 3) 000 001 010 011 100 101 110 111

22. Add Check Bits Notation: (bit 1, bit 2, bit 3, bit 4, bit 5, bit 6) CC0C00 CC0C01 CC0C10 CC0C11 CC1C00 CC1C01 CC1C10 CC1C11

23. Generate the First Check Bit 0C0C000C0C011C0C101C0C111C1C001C1C010C1C100C1C110C0C000C0C011C0C101C0C111C1C001C1C010C1C100C1C11

24. Generate the Second Check Bit 000C00 010C01 100C10 110C11 111C00 101C01 011C10 001C11

25. Generate the third Check Bit 000000 010101 100110 110011 111000 101101 011110 001011

26. Hamming Code 000000 010101 100110 110011 111000 101101 011110 001011 Blue: Check bits Black: Data bits

27. Error in a Data Bit

28. Error in the Check Bit