← IGCSE Computer Science Paper 1

Serial transmission

Sending data one bit at a time, one after another, down a single wire or channel. The bits arrive in the same order they were sent.

Part of: IGCSE Computer Science 0478 — 2.1 Data Transmission Types and Methods — Module 22, WA Computer Science ATAR Year 11 — Network Communications — Module 16

Understanding Serial transmission in IGCSE Computer Science Paper 1

What it does: One wire means all the bits must use the same path, which is why they go one at a time. Because the bits travel in a single line down one wire, the order is kept and the received data matches the sent data. Serial uses a single wire or channel. Using several wires side by side is parallel transmission. One bit at a time is the key idea of serial transmission.

Common mistakes: Serial transmission sends one bit at a time. send(data) would push every bit at once. It should be send(bit) inside the loop. Serial transmission sends one bit per tick down a single wire. Setting 8 bits per tick describes parallel transmission. It should be bits_per_tick = 1.

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This module's key terms are also in a printable crossword (Modules 121–130) and word search (Modules 121–141).

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Learning

Duo

How does serial transmission send data?

Many bits at the same time down several wiresOne bit at a time down a single wire

Matches

Serial transmission sends 8 bits at the same time down 8 wires

↓

This describes parallel transmission. Serial sends one bit at a time down a single wire.

Applying

Meanings

Term

serial transmission

Meaning

Sending data one bit at a time, one after another, down a single wire or channel. The bits arrive in the same order they were sent.

Practice

// Serial: one wire, one bit at a time

Testing

Gaps

wires ←

Check Answer

Spots

2for bit in data:

3 send(data)

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Quick Questions

1. How does serial transmission send data?

A. One bit at a time down a single wire ✓

B. Many bits at the same time down several wires

Serial transmission sends bits one after another down one wire or channel. Sending many bits at once is parallel transmission.

2. How many wires or channels does serial transmission use to carry the data bits?

A. One ✓

B. Eight or more

Serial uses a single wire or channel. Using several wires side by side is parallel transmission.

3. A byte (8 bits) is sent using serial transmission. How are the 8 bits sent?

A. One after another, in a line ✓

B. All 8 together at the same moment

In serial transmission the 8 bits travel one after another, so the byte is sent as a stream of single bits.

4. The bits 1 0 1 1 are sent by serial transmission. What order do they arrive in?

A. Any order, because each bit takes its own path

B. 1 0 1 1, the same order they were sent ✓

With one wire the bits cannot overtake each other, so they arrive in the same order they were sent.

5. Why do bits arrive in order in serial transmission?

A. They travel along different wires at different speeds

B. They all travel along the same single wire ✓

One wire means one queue of bits, so they stay in order. Different wires at different speeds is what causes data skew in parallel transmission.

Match the Pairs

serial transmission → Sending data one bit at a time, one after another, down a single wire or channel

1 0 1 1 0 0 1 0 (sent along one wire) → A byte sent serially: each bit travels in turn and they arrive in the same order they were sent

Serial transmission uses only one wire, so every bit has to share it → wires = 1

In serial transmission the bits arrive in the same order they were sent → sent: 1 0 1 1 / received: 1 0 1 1

Serial transmission sends 8 bits at the same time down 8 wires → This describes parallel transmission. Serial sends one bit at a time down a single wire.

Serial transmission: bits can arrive in a different order than they were sent → In serial transmission the bits arrive in the same order they were sent because they travel one after another on one wire.

Key Term

serial transmission

Sending data one bit at a time, one after another, down a single wire or channel. The bits arrive in the same order they were sent.

Fill in the Blanks

1. MODE ← SERIAL wires ← 1 bitsAtATime ← 1

Hint: Type how many wires serial transmission uses to send its data.

2. FOR i ← 1 TO 8 SEND data[i] ON wire1 NEXT i

Hint: Type the pseudocode keyword that starts a loop with a counter, so bits are sent one after another.

3. sent ← "10110010" received ← sent IF received = sent THEN OUTPUT "In order"

Hint: Type the comparison operator that checks the bits arrived exactly as they were sent.

4. bitsLeft ← 8 SEND nextBit bitsLeft ← bitsLeft - 1

Hint: Type the operator that counts down the bits remaining after each single bit is sent.

5. IF wires = 1 THEN mode ← SERIAL ENDIF

Hint: Type the name of the transmission type that sends bits down a single wire.

Spot the Error

Question 1

A data = "10110"

B for bit in data:

C send(data)

Line C — Serial transmission sends one bit at a time. send(data) would push every bit at once. It should be send(bit) inside the loop.

Question 2

A wires = 1

B bits_per_tick = 8

C ticks = 8 / bits_per_tick

Line B — Serial transmission sends one bit per tick down a single wire. Setting 8 bits per tick describes parallel transmission. It should be bits_per_tick = 1.

Question 3

A data = "1101"

B received = ""

C for bit in data:

D received = bit + received

Line D — In serial transmission the bits arrive in the same order they were sent. Putting each new bit at the front reverses the order. It should be received = received + bit.

Question 4

A data ← "0110"

B FOR i ← 1 TO 3

C SEND data[i]

D NEXT i

Line B — The data has 4 bits and each one is sent separately down the wire. Looping only to 3 means the last bit is never sent. It should be FOR i ← 1 TO 4.

Question 5

A data = "1011"

B for i in range(len(data)):

C print(data[0])

Line C — Each pass of the loop must send the next bit in order. data[0] sends the first bit every time. It should be print(data[i]).

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