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OCR H446 1.4.1 Character sets

Part 9 of 11 · H446 1.4.1 · Data types

Turning characters into numbers and back is the H446 1.4.1 content here, and the worksheet keeps the character set and the encoding as separate ideas. A multilingual group chat supplies the context, and every code comes from a table given in the question, because the assessed skill is using a mapping rather than memorising code values.

Students will:

  • explain why a sender and receiver need a compatible character mapping
  • convert a supplied character code between denary, hexadecimal and binary
  • decode a bit pattern and a hexadecimal code back into characters
  • describe what goes wrong when the same bits are read with an incompatible mapping
  • compare ASCII and Unicode, including a storage or transmission consequence of the encoding chosen

Inside: 7 explanation cells, 1 multiple-choice question, 1 fill-in-the-blanks cell, 3 written answers and 2 number answers. 19 marks, about 35 to 45 minutes.

Series: H446 1.4.1 · Data types, part 9 of 11.

Shared by Coding PathwayVerified teacher

  • 14 cells
  • About 45 minutes
  • CC BY-SA 4.0
  • Shared 31 Aug 2026
  • Updated 3 Sept 2026

Preview

The whole resource, exactly as a class sees it. Answers and marking are held back.

Character sets

A multilingual group chat must turn characters into numbers and back consistently. The mapping and the encoding are related but distinct ideas.

By the end, you will be able to

  • explain why a shared character mapping is needed
  • use a supplied code table in binary, denary and hexadecimal
  • compare ASCII’s repertoire with Unicode
  • avoid the misconception that every Unicode character is always 16 bits

Reactivate: binary and hexadecimal conversion; code values will be supplied.

Concept model: codes need an agreed mapping

A character set maps each supported character to a numeric code. The code is stored as bits. Sender and receiver must use a compatible mapping to interpret the same bit pattern consistently.

ASCII provides a small, historically important set suitable for basic English letters, digits, punctuation and control characters. Unicode defines code points for characters from many writing systems and symbols. Do not claim that Unicode is always 16-bit: encodings such as UTF-8 and UTF-16 represent code points using different numbers of bytes.

Model the communication chain

character → agreed code point → encoded bytes → transmission/storage
                                           ↓
displayed character ← decoded code point ← bytes

For the character A in the supplied mapping, denary 65 = hexadecimal 41 = binary 01000001. These are three notations for the same numeric code.

If a receiver applies an incompatible mapping, the bits have not changed but the displayed character may be wrong. Unicode provides a much wider repertoire; an encoding such as UTF-8 determines the byte sequence.

Supplied code-table excerpt

CharacterDenary codeHex code
A6541
a9761
?633F
£163A3

Use this table; OCR does not expect you to memorise code values.

Guided code-table method

For £ with supplied denary code 163:

  1. convert 163 to hexadecimal: A3;
  2. convert each nibble: A → 1010 and 3 → 0011;
  3. combine: 10100011;
  4. reverse-convert to check 128 + 32 + 2 + 1 = 163.

No memorisation of character codes is required; the skill is using the supplied mapping accurately.

Number systems4 marks

Using the supplied character mapping in each question, give the 8-bit binary code.

a)Give the 8-bit binary ASCII code for 'r'.

Binary

b)Give the 8-bit binary ASCII code for 'N'.

Binary

c)Give the 8-bit binary ASCII code for 'S'.

Binary

d)Give the 8-bit binary ASCII code for 'H'.

Binary
Number systems3 marks

Using the supplied character mapping in each question, give the hexadecimal code.

a)Give the hexadecimal ASCII code for '#'.

Hexadecimal

b)Give the hexadecimal ASCII code for '0'.

Hexadecimal

c)Give the hexadecimal ASCII code for 'R'.

Hexadecimal
Written answer2 marks

Using the supplied table, decode the bit pattern 01000001 and the hexadecimal code A3 into characters.

Convert or look up each numeric code, then give the displayed character.

Students type their answer here.

Multiple choice1 mark

Why is Unicode more suitable than ASCII for a worldwide messaging service?

  • AUnicode guarantees every character uses one byte.
  • BUnicode stores images instead of numeric codes.
  • CUnicode removes the need for an encoding.
  • DUnicode includes code points for a much wider range of writing systems and symbols.
Written answer2 marks

Explain what could happen if a sender encodes a character using one character mapping but the receiver interprets the same bits using a different incompatible mapping.

Connect the stored number to the character displayed.

Students type their answer here.

Written answer3 marks

Compare ASCII and Unicode for the group-chat system. Give one relevant advantage of Unicode and one possible storage or transmission consequence of the chosen Unicode encoding.

Avoid saying that every Unicode character is exactly 16 bits.

Students type their answer here.

Closed-book checkpoint

Complete each sentence from memory. There is no answer bank and correctness is held for teacher review.

Fill in the blanks4 marks
A character set provides a completion 1 from characters to numbers. Unicode defines a much wider completion 2 than ASCII. A Unicode code point still needs an completion 3 such as UTF-8. OCR supplies any code-table values needed for completion 4.

Retrieval check

Explain the difference between a character set and an encoding, convert one supplied code in all three bases, and correct the statement “Unicode is always 16-bit”.