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Kirk Meyer

If you have anything that you would like to have published in this newsletter, please send it to newsletter@ticalc.org. Each month I will print one letter that I choose in the "Letter to the Editor" section. You can send letters regarding just about anything as long as they are constructive. Send your letters to the editor to newsletter@ticalc.org.

In calculator news this month, Icarus Productions has been active. Andreas Ess has released M.C. Mik v1.1u for Usgard and has also released the source code for an RPG he was working on. Additionally, Kirk Meyer has released Emulator86 v0.36, a TI-86 emulator, for Windows 3.1 and Windows 9x. It features *.85? and *.86? file loading, grayscale support, screenshot support, a disassembler, a debugger, a memory viewer, and support for the TI-Graph Link cable.

This is the first of many installments on how to program in assembly language. I will start with the basics and then become more specific. When I deal with the specifics I will use the Z80 as my example for the sake of consistency. The concept of 68000 programming is the same, only the instructions and registers are different. In this installment, I thought I would begin by clearing up some common problems that beginners have with assembly language programming. The first of these is registers. In assembly language, the only things that you can do commands on, like add and subtract, are generally registers. There are very few registers in a microprocessor and they could never hold all of the data that you want them to. This aspect is usually confusing to people who have previously programmed in BASIC, where you have variables that can be easily accessed. In assembly language, you must store your variables somewhere, but that place and how much of it varies from calculator to calculator.

Secondly, I want to give an introduction to the stack. The stack is one way to deal with the relatively small amount of registers by saving some of them for later. Think of the stack as a stack of plates. When you want to save a register for later, write the contents of the register on a plate and put it on top of the stack. Then, when you pick the plate up off the stack, you transfer what is written on the plate into ANY register of your choosing (because the original register is not written on the plate). As we will see at a later time, the stack also helps with calling subroutines.

My tentative plan for future installments is to first talk about the registers in-depth, followed by a discussion of commands that can be performed using the registers. After that I plan to discuss memory and pointers. After that, the direction of this series depends mostly on what people tell me would be most helpful to them, so be sure to send your feedback to kirk@ticalc.org.

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