Data skew in parallel transmission

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Quick Questions

Shade in the A or B circle for each question.

1. What is skew in parallel transmission?

A Bits sent together arrive at slightly different times

B Bits are sent one after another down a single wire

2. Which type of transmission can suffer from skew?

A Parallel transmission

B Serial transmission

3. What can skew cause?

A Data is received incorrectly

B Data is sent faster

4. What happens to skew as the cable gets longer?

A It gets better

B It gets worse

5. Why is parallel transmission only used over short distances?

A Parallel wires cannot carry binary data

B Skew becomes a bigger problem over long cables

Match the Pairs

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

Left column		Right column
1skew		Aif cable_length <= short_distance then use parallel
2Cable length: 1 m -> 10 m		BBits sent together down parallel wires arrive at slightly different times, so the data can be received incorrectly
3Skew means bits sent at the same time over 8 parallel wires do not all arrive together		CThis describes serial transmission, not skew. Skew happens when bits sent together on several parallel wires arrive at different times.
4Because of skew, parallel transmission is only used over short distances		DSent together: 10110010 -> Arrive at different times
5Skew happens because a single wire sends bits one after another		EA longer cable makes skew worse, not better, so parallel is only used over short distances.
6A longer parallel cable reduces skew, so it suits long distances		FThe longer the parallel cable, the bigger the timing differences between wires, so skew gets worse

Definitions

skew

Fill in the Blanks

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

____ = bits arrive at different times

Longer cable = ____ skew

Skew means data is received ___________

Parallel is only used over _____ distances

Skew happens on ________ wires

Spot the Error

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

Question 1

A IF cable_length > 5 THEN

B skew_risk ← LOW

C ELSE

D skew_risk ← LOW

E ENDIF

Question 2

A OUTPUT 'Sent 1 bit at a time'

B OUTPUT 'Wires used: 8'

C OUTPUT 'Skew can occur'

Question 3

A cable ← 'short'

B IF cable = 'short' THEN

C OUTPUT 'Skew is large'

D ENDIF

Question 4

A FOR wire ← 1 TO 8

B SEND bit ON wire

C NEXT wire

D OUTPUT 'Skew is harmless'

Question 5

A cable ← 1

B cable ← cable / 10

C OUTPUT 'Skew gets worse'

Answer Key

Data skew in parallel transmission

Section A: Quick Questions

A — Bits sent together arrive at slightly different times

A — Parallel transmission

A — Data is received incorrectly

B — It gets worse

B — Skew becomes a bigger problem over long cables

Section B: Match the Pairs

skew → Bits sent together down parallel wires arrive at slightly different times, so the data can be received incorrectly

Cable length: 1 m -> 10 m → The longer the parallel cable, the bigger the timing differences between wires, so skew gets worse

Skew means bits sent at the same time over 8 parallel wires do not all arrive together → Sent together: 10110010 -> Arrive at different times

Because of skew, parallel transmission is only used over short distances → if cable_length <= short_distance then use parallel

Skew happens because a single wire sends bits one after another → This describes serial transmission, not skew. Skew happens when bits sent together on several parallel wires arrive at different times.

A longer parallel cable reduces skew, so it suits long distances → A longer cable makes skew worse, not better, so parallel is only used over short distances.

Section C: Definitions

skew — Bits sent together down parallel wires arrive at slightly different times, so data can be received incorrectly. It gets worse as the cable gets longer.

Section D: Fill in the Blanks

skew = bits arrive at different times

Longer cable = more skew

Skew means data is received incorrectly

Parallel is only used over short distances

Skew happens on parallel wires

Section E: Spot the Error

B — Skew gets worse as the cable gets longer, so a long cable (more than 5) should set skew_risk to HIGH, not LOW.

A — Parallel transmission sends several bits at once down several wires. Sending one bit at a time describes serial. It should say 'Sent 8 bits at once'.

C — Over a short cable the bits have little time to drift apart, so skew is small. It should output 'Skew is small'.

D — Skew is not harmless. Bits arriving at slightly different times can make the data be received incorrectly. It should say 'Skew can corrupt data'.

B — The program shows skew getting worse, which happens when the cable gets longer. The cable length should be multiplied (cable * 10), not divided.