Fred 8

Machine Code Made Easy - Part 3

Bonjour! Mes petits choufleurs, et bienventure.
Yes, ‘tis I again with part 3 (yup, THREE!) of the series. Today
we shall be looking at somethings I hope will be of relevance to
all you budding coders out there. After a short bit on ports,
we’ll head straight into building a program.

But first in this 15 page bumper issue…

PORTS
======

Ports are the vital parts of your coup‚ that allow you to
talk to it from the keyboard, joystick, mouse etc. They also
allow your coupe to talk back to a printer, tape recorder etc.
So, as you can see we need a way in machine code to control
what goes in (INPUT) and comes out (OUTPUT) from them.
Your coupe can address 64k (that’s 65536) of ports, and the
commands for doing so are pretty simple:

IN (xx),A ; ( must be A )
OUT (xx),A ; ( or B or C or D etc )

xx can be any 8-bit port number.

“Hmmm,”I hear you cry.”How do we get a 16 bit number into an 8 bit one?”
Well, the way in which it works is quite complicated, but to make matters
easier I shall present a simple method: Firstly,
most of the useful ports lie between 0 and 255, so this ain’t a problem.

Fred 7

Machine Code Made Easy - Part 2

Hello again eveyone! ‘Tis I, the Wizard, here to enlighten all
you beginners as to the joys of machine code. This is part 2 in
the series, and I will be referring back to part 1, so if you
don’t have FRED6 (why not?) go and order a copy immediately!

Right, let us proceed….

A - THE MATHS LESSON
———————————

If you hope to get anywhere in m/c a basic knowledge of
binary and, to a lesser extent, hexadecimal, is neccesary.
BINARY is base 2 - a series of 1’s and 0’s which can
represent any number you care to think of. This is how numbers
are stored inside your coupe, so this is important.
Each binary digit (or BIT) stÍ.ands for a power of 2:1,2,4,8…
and so 8 bits can hold a number between 0 and 255.
This is how they are arranged:
7 6 5 4 3 2 1 0 -> BIT number
———————————————-
128 64 32 16 8 4 2 1 -> POWERS OF 2
———————————————-
1 0 0 0 1 0 1 1

Fred 6

Machine Code Made Easy - Part 1

Hello everyone out there in Coup‚ land. This is (hopefully!) the
first in a series on machine code for beginners. No, please,
don’t all groan at once - m/c has its uses - it’s not just for
swotty egg-headed squares. Just think of all the games you’ll
write and all the money you’ll make after reading this article!
Now, firstly you’ll need an assembler. This is a program with
which the machine code can be entered. I can ..recommend the one
from LERM although any old one’ll do. Got one? Right. Now to
lesson one…..

REGISTERS:-

The first thing we’ll deal with are the registers.
You could compare these with variables from BASIC, and there are
8 main ones. They are named after letters: A;B;C;D;E;F;H;L and
each can contain a number between 0 and 255

To allocate a number to one of these registers we use the
command: LD A,100

This stands for LoaD A with 100 and is
like the BASIC: LET A=100
The contents of one register can be copied into another by
using : LD A,B

This will load A with whatever is in B
and is like : LET A=B in BASIC
Although each register can only hold a number 0 to 255,
they can be used in pairs to hold a numbe..r 0 to 65535. The
pairings used are: B&C ; D&E ; H&L ; A&F
The F register is special and is used to store the results
of tests via FLAGS (F for flag, geddit?) and so shouldn’t be
tampered with. A flag is just a binary digit which indicates
whether a calculation has produced a carry or a zero and things
like that. Don’t be concerned with flags for the moment.
2 other registers we will use are IX and IY. These are known
as INDEXES and can hold a number 0 to 6..5535.

Issue 2

Issue 1

Item	Author	Description
Magazine	Steven Pick, Andy Nibbs, Tim Newman, Mark Johnson
SAM News (News)	Steven Pick	A Welcome to the Very First Issue of SAM News
SAM News (Addresses)
Font 1 - Digi
Font 2 - Marbles
Screen Menu
Demo - Audio
Demo - Visual
Game - Micropuzzle
Tech Tips
Help!
Next Month…
Editorial		» login or register to post comments | read more Peter Gallagher Submitted by PGallagher69 on Wed, 2017-09-13 11:37. Title image: Biography: Sam Coupe fan and Amateur Programmer. Published a couple of Lemmings themed demo’s in FRED Magazines 19 and 22… Including an animation and musical Advert. Where are they now?: Software and IT Consultant for PJG Creations Ltd, living in Loughborough. Proud owner of a SAM Coupe once again! » login or register to post comments | read more SAM copyrights Submitted by C Jordan on Sun, 2017-04-16 11:40. Copyrights Story: I give permission for the following SAM programs to be available for download - Five On a Treasure Island, Splat!, SAM Adventure System. C. Jordan. » 2 comments | read more first page previous page 1 2 3 4 5 6 7 8 9 ... next page last page	Poll Megademo: Stupid Pointless Cool You could have spent all that time writing a game! Oooh, interesting, I wonder how they did that? Wow, I never knew my Sam could do that! Meh, that's not as good as Lyra III... 13 comments | older polls | results Syndicate