z80 game development

This is a collection of tutorials on developing games in z80 assembler for the TI calculators. While focused on the TI86, much of this applies to any z80-based TI calculator: TI85, TI83/+, TI84/+, TI82.

• Beginner - getting started with assembler code, registers, arithmetic, flags, and memory
• Intermediate - more details on the beginner topics
• Graphics - manipulating pixels and grayscale
• Advanced - ports, hidden TI-OS features
• Opcodes - listing of all z80 opcodes (numeric or alphabetic)
• Variables - manipulate TI-OS variables
• Menus - creating native TI-OS menus
• Design - planning and game design, writing clean code
• Downloads - tools, examples, algorithms

Beginner

• Number Bases - Learn how to understand and convert between the different number systems such as binary and hexadecimal. Make your calculator do all the work.
• z80 Processor - History and specifications of the z80 processor. What’s really behind the games.
• TI86 Specs - Basic information about the TI86, ROM versions, and the LCD.
• Format and Compiling - Start coding. Get the necessary tools to get you on your way. Walk through creating your first program and running it.
• Oh, No! It Crashed! - What to do when it freezes up on you. A step-by-step diagnosis.
• TI-BASIC versus Asm - A simple chart to show you equivalent tasks in z80 asm and the old TI-BASIC.
• Aliases - Equates and include files. Download the hottest include files around. Make your own equates.
• Registers - How to store and manipulate values.
• Instructions - Start working up your own programs. Learn the basic syntax of assembler instructions. A great place to reference all those little mnemonics and what they do.
• Flags and Conditions - if statements.
• Math - Learn the basics of simple math routines like multiplying, dividing, adding, and subtracting.
• Two’s Compliment - Negative numbers and how to use them.

Intermediate

• Logical Operators - Introduction to and, or, and xor. How to mask out bits and control binary data.
• Miscellaneous Instructions - These don’t fit in anywhere? neg, scf, and others!
• All the Flags - Besides the zero and carry flags, there are four others! What do they all do? Come find out!
• Restart Commands - Faster calls with the help of these one byte instructions used for some of the most frequent ROM calls.
• Memory and Pages of It - Dive into the memory of your calculator. What is Consecutive Addressing and how to reference addresses in memory. Explore some safe areas to store data at!
• Variables - Start off storing user input and data like high scores and such.
• The Stack - Ever heard of "Last On, First Off"? Save register pairs and recall their values later with push and pop!
• Tables and Arrays - The famous for loop used in recursion. Take advantage of the ix and iy register pairs for lists with an intro into matrices!
• Simulated 16-bit Addition - A faster method of adding a to hl. In time crunch areas, this beats conventional methods.
• Random Numbers - Need a random number? This is the place for you! Take your pick of different routines, all designed to give you a different number each time.
• TI’s ROM Calls - Why draw up your own routine when TI’s already got a ton. Use their calls for printing text, checking keypresses, clearing the screen, and much much more!
• Getkey - Get user input in a flash with _GetKey! This routine gives you the ability to respond to certain key presses. Here you’ll find charts filled with key press codes with their equates, a handy reference!
• Program Counter, Stack Pointer - Two fundamental registers the z80 uses to keep track of executing code.
• Text Display - Print text on the screen in an instant with your choice of several routines printing everything from individual characters to entire paragraphs. Learn how to print in standard or small text with a look at how to create your own custom fonts.
• Down-Left Bug - Why does the calculator freeze when you press down-left?

Graphics

Pixel manipulation and sprite animation. Line-by-line walk throughs of the most popular graphics routines.

• The Screen - Introduction to the LCD, Video Memory, and how the pixels are stored in memory.
• Find Pixel - Find where on the screen pixels are supposed to be from manipulating the coordinates.
• Pixel Manipulation - Setting, reseting, and testing pixels using Find Pixel.
• Sprites - Printing small images on the screen.
• Tile Maps - Draw game levels on the screen using compact level data.
• Grayscale Graphics - Blend black and white to make gray. Check out this line-by-line analysis of one of the hottest Grayscale routines out there.

Advanced

• More Registers - Now you have even more with the addition of a whole hidden set of registers banks. Also, learn about the Index and Refresh Registers.
• Reading Keys from Port - Don’t wait up for that slow _GetKey, scan for keys in an instant with Port 0. You can always count on the Ports for quick results. Also included, a handy reference table with key bitmasks for every key.
• Assembler Directives - Customize your source code in a flash with macros. Reference just about every directive available for the TASM Assembler.
• On-Off - Turn your calculator On or Off in a flash using the ports. Even put it in low power mode to conserve energy. Take a peek at how TI-OS turns itself On and Off.
• Shift and Rotate - Move bits left or right within a byte. This handy reference provides examples and graphical representations of what each instruction does!
• Entry Stack - Access and manipulate the user input history.
• Morphic Code - Programs that edit themselves, what a dream! Preload code with values, manipulate routines, and more.
• All the Ports - Communicate with the z80’s hardware behind the scenes. Change the Video Screen address, adjust the contrast, change the power mode, etc.
• Square Root Programs - Take command of the many common tasks of TI-OS such as Parsing, Tokenizing, _GetKey, Graphing, and much much more! TI-OS lets you run your own programs before or after it performs these tasks. Step in and manipulate data before TI-OS gets it.
• System Flags - Want a complete listing of TI-OS’ flags? You got it! This reference gives you everything you need to know about customizing the options of TI-OS from Graph Methods to Operand calculations.
• Auto Power Down - Like a screen saver, TI-OS will shut down after inactivity. Learn how to control this process and use it to your advantage.
• Sound - How to produce mono sound with a few small parts. These step-by-step instructions walk you through the process of building speakers and then programming sound into your games. You can even convert Wave files.
• Simulating Key Presses - Kind of like macros, have the TI86 think you’re pushing keys and respond to them when you’re not even touching the calculator.
• Fonts - Create your own fonts for TI-OS to for everything.
• Interrupt - Create your own routine to be run about 200 times a second in the background of regular code.
• Interrupt Mode 1 - Run a routine 200 times a second to perform background tasks.
• Interrupt Mode 2 - Run a routine randomly chosen from a jump table 200 times a second.

Opcodes

• Overview
• Sorted by value
• Sorted by name

Variables

• TI86 Variable Manipulation - Manipulating data behind TI-OS’ back. What are the Operator Registers?
• Variable Name Format - How to set-up variables’ names in the OP Registers. Learn about the Variable Type byte with the included reference chart and numerous full examples.
• Creating Variables - You can generate just about any variable type you want through these asm calls.
• _FindSym - The basis for all variable manipulation, _FindSym finds variable data addresses fast. A must for all who want to work with TI-OS variables!
• Absolute Addressing - A 24-bit address? That’s right! Since there’s more than 64 kilobytes of memory, you need to be familiar with TI’s method of absolute addressing. It’s used all the time with TI-OS variables.
• Messing with Data - This is the meat of the topic: How to manipulate the data within the TI-OS Variables! Through step-by-step examples, you’ll learn how to edit everything from Lists and Complex Matrices to Real Numbers and Strings! You can even download source code for Tokenized, Un-Tokenized, and Assembler Programs.
• Binary Coded Decimal - Format Floating Point decimal numbers. Work with exponents, Complex and Real numbers, and negative numbers. Examples are illustrated in tables and code snippets!
• VAT Searches - Learn the methodology behind the Variable Allocation Table and how to search through it. You can even walk through the line-by-line analysis of one of the hottest search routines out there! Learn how to make your own shell.
• External Levels - Access and execute other variables on the calculator as level data, plug-ins, and much more. Customizable, full-featured programs are just around the corner.
• OP_ Math - Get an understanding of how to perform Floating Point math with the Operator Registers. You can even check out TI’s own routine to input strings or values.

Menus

Create full featured, native TI-OS Menu Trees. Have one on the bottom like the Custom Menu or branch that one out into other Menu Trees. Create a menu with conversions, constants, program names, and more.

• Executing Menus - The place to start, here you’ll learn about two routines that tie up the whole process. It’s as simple as loading a pointer!
• Creating Menus - Here’s where the full customization of the menus comes into play. Create multiple menus with Paste, Branch, or Execute Items!
• ROM Menus - Take advantage of TI’s own menu structures. Use them as patches for your own structures!

Design

• The Design Process - Take a walk through designing a game. Go step-by-step as you create a well designed game that will last for ages. Great design is essential for great games.
• Clean Code - A must read for all programmers, this section gives details and examples of what to do and what not to do. These key points will change the way you program.

Dedicated to those who taught me

Dux Gregis, Jimmy Mårdell, Jay Hellrungen, Patrick Davidson, Jonah Cohen, Kirk Meyer, David Phillips, Alan Bailey, Adrian Mettler

This content was formerly hosted as “The Guide” on TI-Calc.org.