Parity byte

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Quick Questions

Shade in the A or B circle for each question.

1. Where is the parity byte sent in a block of data?

A After the data bytes of the block

B Before the first data byte

2. What does each bit of the parity byte act as the parity bit for?

A One column (bit position) down all the bytes

B One row (a single data byte)

3. A block has 6 data bytes. How many parity bytes does the block use?

A One parity byte for each data byte

B One parity byte for the whole block

4. Which statement describes column parity?

A Bit 0 of the parity byte checks all 8 bits of the first data byte

B Bit 0 of the parity byte checks bit 0 of every data byte

5. The data bytes are 8 bits long. How many bits does the parity byte have?

A 8 bits, one for each column

B 1 bit, for the whole block

Match the Pairs

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

Left column		Right column
1Column 1 down: 1,0,1 -> parity bit 0		AThe parity byte is sent before the data bytes. It must be sent after them, as the last byte of the block.
2BYTE1 BYTE2 BYTE3 PARITYBYTE		BThe parity byte is sent after all the data bytes in the block, as the last byte.
3One parity byte is sent for the whole block of data bytes, as the last byte (even parity).		C10110010 01100001 11000111 00010100
4Each bit of the parity byte is worked out by counting the 1s down one column of the block.		DColumn 6 down: 0,0,1 -> parity bit 1
500010100 10110010 01100001 11000111		EBit 1 of the parity byte comes from the first bit of every data byte. Two 1s is even, so with even parity this bit is 0.
6Parity byte bit 1 = parity of 10110010		FThis uses one data byte (a row) instead of a column. Bit 1 of the parity byte must come from the first bit of every data byte.

Definitions

parity byte

Fill in the Blanks

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

SEND data bytes SEND ______ byte

Column 1 bits: 1, 0, 1, 1 Even parity bit for column 1 = _

Each parity byte bit checks one ______

data bytes in block = 4 parity bytes needed = _

Column 3 bits: 0, 0, 1, 0 Odd parity bit for column 3 = _

Spot the Error

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

Question 1

A Byte 1: 10110010

B Byte 2: 01101100

C Parity: 11011010

Question 2

A Parity byte: one per byte

B Each bit covers one column

C Sent after the data bytes

Question 3

A Byte 1: 11000011

B Byte 2: 10100000

C Odd parity byte: 01100011

Question 4

A Byte 1: 10000001

B Byte 2: 00110000

C Byte 3: 01010101

D Parity: 11100110

Question 5

A FOR each column (even parity)

B COUNT the 1s along each byte

C IF the count is odd

D PRINT error found

Answer Key

Parity byte

Section A: Quick Questions

A — After the data bytes of the block

A — One column (bit position) down all the bytes

B — One parity byte for the whole block

B — Bit 0 of the parity byte checks bit 0 of every data byte

A — 8 bits, one for each column

Section B: Match the Pairs

Column 1 down: 1,0,1 -> parity bit 0 → Bit 1 of the parity byte comes from the first bit of every data byte. Two 1s is even, so with even parity this bit is 0.

BYTE1 BYTE2 BYTE3 PARITYBYTE → The parity byte is sent after all the data bytes in the block, as the last byte.

One parity byte is sent for the whole block of data bytes, as the last byte (even parity). → 10110010 01100001 11000111 00010100

Each bit of the parity byte is worked out by counting the 1s down one column of the block. → Column 6 down: 0,0,1 -> parity bit 1

00010100 10110010 01100001 11000111 → The parity byte is sent before the data bytes. It must be sent after them, as the last byte of the block.

Parity byte bit 1 = parity of 10110010 → This uses one data byte (a row) instead of a column. Bit 1 of the parity byte must come from the first bit of every data byte.

Section C: Definitions

parity byte — An extra byte sent after a block of data bytes. Each of its bits is the parity bit for one column (bit position) taken down across all the data bytes in the block.

Section D: Fill in the Blanks

SEND data bytes
SEND parity byte

Column 1 bits: 1, 0, 1, 1
Even parity bit for column 1 = 1

Each parity byte bit checks one column

data bytes in block = 4
parity bytes needed = 1

Column 3 bits: 0, 0, 1, 0
Odd parity bit for column 3 = 0

Section E: Spot the Error

C — Column 6 holds 0 and 1, which is one 1. Even parity needs the parity bit to be 1 so the column total is even. The parity byte should be 11011110.

A — A parity byte is not made for each data byte. One parity byte is made for the whole block of data bytes.

C — 01100011 is the even parity byte. With odd parity each column, including the parity bit, must hold an odd number of 1s. The correct parity byte is 10011100.

D — Column 7 is 0, 0, 0 with no 1s, so even parity needs a parity bit of 0. The parity byte should be 11100100.

B — A parity byte is checked column by column. The 1s must be counted down each column across all the bytes, not along each byte.