7

Getting retro with the Z80: software

TUTORIAL

Dive into Z80 assembly language

Getting retro with the Z80:

software

ast month, we built a Z80 computer

on a breadboard. This month, we’re

going to take a look at how to program

it using assembly language. Assembly

language is a symbolic version of

machine code. It uses names for the

instructions, registers, condition flags, etc. It also

allows you to label addresses in the code or data

and refer to the labels in the code rather than the

numeric addresses. The idea behind assembly

language is to provide a one-to-one mapping to

machine code, while being far more readable and

writable than a series of bytes.

TEMPORARY STORAGE

Every CPU has registers to store values that can

then be operated upon. The Z80 has a fairly rich

set of registers for an 8-bit CPU. It has an 8-bit

accumulator (called A), as well as six other general

purpose 8-bit registers: B, C, D, E, H, and L. These

six have the added utility that they can be used

in pairs (BC, DE, and HL) as 16-bit registers. That

allows working directly with addresses inside the

CPU in a very flexible and powerful way. Two other

important registers are the 16-bit index registers, IX

and IY. These let us do powerful array and structure

type operations very easily. We won’t be using them

L

YOU’LL NEED

z80pack

hsmag.cc/sWCRQK

Dave Astels

@dastels

Dave’s career started
in the 8-bit days, with
the Z80 and 6502, and
he’s been working with
computers ever since.
He does some writing
at daveastels.com and
learn.adafruit.com.

Above

You can build your

own system or

get a kit such as

this RC2014