Parity block check

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Quick Questions

Shade in the A or B circle for each question.

1. In how many directions does a parity block check test the data?

A One: across the rows only

B Two: across the rows and down the columns

2. What does the parity byte in a parity block hold?

A One parity bit for each column of the block

B A copy of the first byte in the block

3. Even parity block: the byte 10110010 is one row. Which parity bit does it need?

A 0, because it already has four 1s

B 1, because it already has four 1s

4. In an even parity block, a column has 1, 1, 0, 1 in its data bytes. What is that column's bit in the parity byte?

A 0, because the column already has an even number of 1s

B 1, to make the number of 1s even

5. After transmission, row 3 and column 5 both fail the even parity check. Where is the error?

A At the single bit where row 3 and column 5 cross

B In every bit of row 3 and every bit of column 5

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1Row 3 fails, column 5 fails		AThe error is in the bit where row 3 and column 5 cross, so that bit can be found and flipped
21011001 0		B11010001
3Even parity row: the data 1101000 has three 1s, so the parity bit must be 1 to make the total even		CWithout a parity byte for the columns, the block is only checked in one direction. The row is found but not the column, so the wrong bit cannot be pinpointed.
4Parity byte: a column holding 1, 0, 1, 1 has three 1s, so its bit in the parity byte is 1 under even parity		DColumn 1,0,1,1 -> parity 1
5Block check = parity bit on each row only		EThe byte has five 1s, which is odd, so it fails an even parity check. Even parity needs an even number of 1s.
6Even parity: 10110011 passes		FAn even parity row: data has four 1s, so a parity bit of 0 keeps the total even

Definitions

parity block check

Fill in the Blanks

Complete each line of code by filling in the missing parts.

Row 1: 1011001 _

Column bits 1,1,0,1 give parity bit _

Parity block: a bit per row, a byte for _______

Row 3 and column 5 fail: flip bit (3, _)

0110 | 0 1011 | _ 1101 | 1

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A Row1: 10100011

B Row2: 11001100

C Row3: 01110000

D Par: 00011110

Question 2

A Even parity block

B Row1: 01001010

C Row2: 10011100

D Row3: 11100111

E Par: 00010001

Question 3

A Row1: 11110000

B Row2: 00011110

C Row3: 10000111

D Par: 01101011

Question 4

A Row1: 00001111

B Row2: 10111010

C Row3: 01100110

D Row4: 11111100

E Par: 00111111

Question 5

A Receive the block of bytes

B Check each row's parity bit

C Skip the parity byte columns

D Error is where they cross

Answer Key

Parity block check

Section A: Quick Questions

B — Two: across the rows and down the columns

A — One parity bit for each column of the block

A — 0, because it already has four 1s

B — 1, to make the number of 1s even

A — At the single bit where row 3 and column 5 cross

Section B: Match the Pairs

Row 3 fails, column 5 fails → The error is in the bit where row 3 and column 5 cross, so that bit can be found and flipped

1011001 0 → An even parity row: data has four 1s, so a parity bit of 0 keeps the total even

Even parity row: the data 1101000 has three 1s, so the parity bit must be 1 to make the total even → 11010001

Parity byte: a column holding 1, 0, 1, 1 has three 1s, so its bit in the parity byte is 1 under even parity → Column 1,0,1,1 -> parity 1

Block check = parity bit on each row only → Without a parity byte for the columns, the block is only checked in one direction. The row is found but not the column, so the wrong bit cannot be pinpointed.

Even parity: 10110011 passes → The byte has five 1s, which is odd, so it fails an even parity check. Even parity needs an even number of 1s.

Section C: Definitions

parity block check — Checks a block of bytes in two directions: a parity bit on every byte (row) and a parity byte for the columns, so the wrong row and column pinpoint the error.

Section D: Fill in the Blanks

Row 1: 1011001 0

Column bits 1,1,0,1 give parity bit 1

Parity block: a bit per row, a byte for 
columns

Row 3 and column 5 fail: flip bit (3, 5)

0110 | 0
1011 | 1
1101 | 1

Section E: Spot the Error

C — This is an even parity block. The data 0111000 has three 1s, so the parity bit must be 1 to make the total even. The row should be 01110001.

B — Row1 now has three 1s, which is odd, so it breaks even parity. The correct row is 01101010, which has four 1s.

D — The parity byte must make every column even. Column 7 has two 1s (rows 2 and 3), so its parity bit must be 0. The byte should be 01101001.

B — A bit in Row2 has changed, so the row now has five 1s (odd) and fails even parity. The row should be 10101010 with four 1s.

C — A parity block check works in two directions. The columns must be checked as well as the rows, otherwise the column of the error cannot be found. The line should say to check the parity byte columns.