Question

Exercises 21-60 are programs or shortanswer questions. Write a program in Pep/9 machine code to output the word "home".

Short answer

The program outputs "home" using Pep/9 machine code by loading each letter's ASCII value into the accumulator and using STRO to display it.

Step-by-step solution

Understand Pep/9 Basics

Pep/9 is a teaching tool that simulates a basic computer system. It operates using a simple assembly language and machine code. Knowing the instructions and how to input them into the Pep/9 system is crucial for programming.

Identify ASCII Values

Each letter in the English alphabet is associated with a specific ASCII code. For the word "home", the letters 'h', 'o', 'm', and 'e' correspond to the ASCII values 104, 111, 109, and 101 respectively.

Prepare Output Instructions

To output a character in Pep/9, use the "STRO" (Store Output) instruction. It outputs the character corresponding to an ASCII value stored in an accumulator or a specified memory address.

Plan the Memory and Instructions

Decide where in memory to place the ASCII codes for 'h', 'o', 'm', and 'e'. Write the Pep/9 machine code to load these values and output them using the appropriate machine instructions.

Write Machine Code

Using Pep/9 machine instructions, the program will sequentially load each character into the accumulator and then use STRO to display it: 1. **Load 'h':** Load Accumulator with 104. 2. **Display 'h':** STRO from Accumulator. 3. **Load 'o':** Load Accumulator with 111. 4. **Display 'o':** STRO from Accumulator. 5. **Load 'm':** Load Accumulator with 109. 6. **Display 'm':** STRO from Accumulator. 7. **Load 'e':** Load Accumulator with 101. 8. **Display 'e':** STRO from Accumulator.

Write Program in Pep/9 Notation

Convert the instructions into the proper machine code format for Pep/9: - `LDA #104` ; Load 'h' - `STRO` ; Output 'h' - `LDA #111` ; Load 'o' - `STRO` ; Output 'o' - `LDA #109` ; Load 'm' - `STRO` ; Output 'm' - `LDA #101` ; Load 'e' - `STRO` ; Output 'e' - `STOP` ; Halt execution

Test the Program

Run the machine code in the Pep/9 simulator to ensure it correctly outputs the word "home". Check each character is displayed as expected in the output console.

Key concepts

ASCII values

ASCII, short for the American Standard Code for Information Interchange, is a character encoding standard used in computers and digital devices. Each character, whether it be a letter, numeral, or symbol, is assigned a unique numeric code. For example, the ASCII value for the lowercase letter 'h' is 104, 'o' is 111, 'm' is 109, and 'e' is 101.
In programming, knowing these values is essential for converting between characters and their numerical representations. ASCII values are often used in low-level programming, such as machine code and assembly, to manipulate text and other characters. This is because these languages interact more directly with computer hardware, which operates using numerical data.
Thus, understanding ASCII codes helps in writing instructions that can precisely control how a computer displays or processes text.

Pep/9 STRO instruction

The Pep/9 system is an educational tool for learning the fundamentals of computer architecture and assembly language programming. One vital instruction in this system is STRO, which stands for Store Output. The STRO instruction allows the Pep/9 machine to output the character represented by an ASCII value stored in a specific register, such as the accumulator.
To use STRO effectively, a programmer needs to first load the accumulator with the desired ASCII value. Once loaded, the STRO instruction will take the value from the accumulator and display the corresponding character to an output device like a screen.
This process simulates how actual computer systems handle character output, providing a hands-on approach to understanding computer operations at a fundamental level. By mastering such instructions, students gain valuable insight into the workings of computer programs and systems.

Assembly language programming

Assembly language programming is a form of low-level programming that serves as an intermediary between high-level languages and machine code. Each assembly language is specific to a particular computer architecture, providing a human-readable format for writing machine instructions.
Compared to high-level languages like Python or Java, assembly language gives programmers more direct control over a computer's hardware. This increased control allows for optimization of performance but requires detailed knowledge of the computer's instruction set architecture.
In an educational context, using assembly language like that in the Pep/9 environment helps students understand the core principles of how computers operate, including how logic gates and processors execute instructions. It is an essential part of computer science education, illustrating the structure and function of digital systems.

Computer science education

Computer science education spans a wide array of topics, from theory to applications. An important component is understanding computer architecture and programming at a fundamental level. This includes learning languages closer to the machine, like assembly or machine code, which provide a deep insight into how software interacts with hardware.
Tools like the Pep/9 simulator are used in educational settings to give students hands-on experience with these concepts. They serve as virtual platforms where students can write, test, and debug low-level programs safely.
This foundational knowledge is not just for future programmers. It is crucial for anyone studying computer science or related fields because it uncovers the principles behind software development, system operations, and the capabilities of digital technology. Mastering these basics enables students to build more complex systems and understand new technologies as they evolve.