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1CP2-P-2.6 Character sets and 7-bit ASCII

Part 6 of 7 · 1CP2-P-2 · Signed data and encoding

The character set worksheet, following the route from character to code to binary and back.

Students will:

  • explain how a character becomes a code and then a binary pattern
  • derive nearby ASCII codes using the alphabetic offset
  • connect character codes to what a short Python listing outputs
  • state one limitation of 7-bit ASCII
  • recommend and justify an encoding for names in many scripts

Inside: 7 explanation cells, 3 multiple-choice questions, 1 number cell, 1 fill-in-the-blanks cell and 4 written answers. 20 marks, about 45 minutes.

Series: 1CP2-P-2 · Signed data and encoding, part 6 of 7.

Shared by Coding PathwayVerified teacher

  • 16 cells
  • About 45 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026

Preview

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

Character sets and 7-bit ASCII

A character set is an agreed collection of characters and their numeric codes. A computer stores each code as binary. Pearson requires understanding of 7-bit ASCII, which provides 2^7 = 128 possible codes.

1. Character → code → binary

Suppose an ASCII table states A = 65. Convert 65 to 7-bit binary:

64 32 16 8 4 2 1 1 0 0 0 0 0 1

So A is 1000001 in 7-bit ASCII. If displayed in an 8-bit storage box it may appear as 01000001; the leading zero does not change the 7-bit code.

Fill in the blanks3 marks
Seven bits provide gap 1 possible patterns. ASCII assigns a numeric gap 2 to each character, and the computer stores that code in gap 3.
  • 7
  • 128
  • binary
  • code
  • hexadecimal

2. Derive nearby codes

Uppercase letters have consecutive ASCII codes. If A = 65, then B = 66, C = 67 and so on. Lowercase letters form a different consecutive range; a does not share the code for A.

Use the stated reference code and count the alphabetic offset. Do not rely on memorising an entire table.

Written answer4 marks

Given uppercase M has ASCII code 77, derive the denary codes for P and J. Show each alphabetic offset.

Count forward three places to P and backward three places to J.

Students type their answer here.

3. Connect codes to Python

Pearson's PLS includes ord(char), which returns the integer code for one character, and chr(integer), which returns the matching character. For characters in the original ASCII set, these functions use the familiar ASCII numeric values.

Read this listing without executing it:

letter = "G"
code = ord(letter)
next_letter = chr(code + 1)
print(code)
print(next_letter)

Predicting first provides evidence that you understand the code rather than obtaining the answer by running it.

Multiple choice1 mark

Which option gives the two outputs in order?

  • A`70`, then `G`
  • B`71`, then `G`
  • C`71`, then `H`
  • D`72`, then `H`
Written answer2 marks

Explain how the program derives the second output from the first code value.

Refer to the consecutive uppercase codes and the role of `chr()`.

Students type their answer here.

4. Convert characters and codes

The native grid below displays ASCII using eight boxes for the platform layout. Treat the leftmost bit as a leading zero: the assessed content remains the 7-bit ASCII code.

Number systems3 marks

Give the 8-bit displayed binary form of each ASCII character.

Use a leading zero followed by the character's 7-bit ASCII code.

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

Binary

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

Binary

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

Binary

5. Limitations and wider encodings

With only 128 codes, 7-bit ASCII cannot represent the full range of writing systems and symbols used worldwide. Encoding systems using more bits can provide many more code patterns. Unicode supplies a much wider shared repertoire.

Do not say ASCII cannot represent any letters or punctuation; it represents a limited selection, mainly suited to English-language computing.

Written answer3 marks

Explain one limitation of 7-bit ASCII and how an encoding system using more bits addresses it.

Connect bit width to the number of available codes and then to representable characters.

Students type their answer here.

Multiple choice1 mark

Which statement accurately describes standard 7-bit ASCII?

  • AIt provides 128 codes, including 32 control codes.
  • BIt provides 255 printable English letters.
  • CIt can represent every writing system without another encoding.
  • DIt assigns the same numeric code to every character.
Written answer2 marks

A school system must store names written in many different scripts. Recommend ASCII or Unicode and justify the choice.

Link the likely characters to code-space capacity.

Students type their answer here.

Multiple choice1 mark

What does an ASCII binary pattern represent directly?

  • AA pixel colour
  • BA character's numeric code
  • CA processor instruction only
  • DA file's compression ratio

Route forward

You can now explain 7-bit ASCII, derive nearby codes and justify wider encodings. The checkpoint retrieves two's complement, shifts, hexadecimal and character representation.