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Chapter 2

Introduction to Looping

2.1 Objective

To become familiar with elementary loops and simple input/outputs functions.

2.2 Simple Input/Output

One of the basic functionality provided by any operating system is input/output

routines. BUFFALO provides several useful functions for performing input/output.

In this lab, we will look at two output functions provided by BUFFALO. Unlike in

high level languages, functions in machine language are known by their addresses.

The two functions we will be using are in ROM at locations $FFB8 and $FFBB

Rather than use these hard to remember and hard to recognize numbers, it is

customary to give them meaningful names. Unless you have a good reason to do

otherwise, it is best to use the name suggested by the vendor, in this case Mo-

torola. The ’oﬃcial’ names for these functions are OUTA and OUT1BYT respectively.

In assembly language, we make the connection between a name (technically known

as a label) and a value using the EQU command as shown

OUTA EQU $FFB8

OUT1BYT EQU $FFBB

NOTE: Labels should be written starting from column 1. If a line does not have

a label, it should start with a space or a tab or a comment character.

We will indicate HEX values with the preﬁx $. However, data that you would be entering

in BUFFALO, as part of memory modify or register modify will be shown without the preﬁx $

although it will be understood that the numbers are written in HEX.

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 100 101

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Motorola Axiom CMD11E1 Guía de usuario Pagina 15