SECTION 1
SYSTEM DESCRIPTION
Sub-Section LIST OF CONTENTS Page No.
1 Introduction 1.1
2 Architecture 1.1
3 Z80A CPU 1.2
4 Memory Organisation 1.4
Read/Write Operations 1.4
5 Input/Output 1.6
TV Picture Generation 1.6
Keyboard Scanning 1.8
Tape Interface 1.10
6 Power Supplies 1.11
Circuit Diagrams
ZX Spectrum, Issue 2 Fig. 1.4
ZX Spectrum, Issue 3 Fig. 1.5
1. INTRODUCTION
1.1 A block diagram of the complete ZX SPECTRUM micro-computer is given in
Figure 1.1. It is valid for all build standards, fitted with either
16k or 48k bytes of dynamic RAM memory. Although functionally
identical, detailed circuit changes have been introduced to improve
reliability and to assist with manufacture. The printed circuit board
layout has also been modified. Details of these changes are
highlighted where necessary in the following paragraphs, and in later
sections referring to fault diagnosis and repair.
2. ARCHITECTURE
2.1 The
architecture
of the
Spectrum
shown
in
Figure
1.1 is
typical
of
many
microcomputer systems
in
that
it
comprises
a
single
microprocessor board
(in
this
instance
a
Z80A
or u 780
CPU),
a
read
only
memory
(ROM),
an
expandable
RAM
memory
and an
input/output
section handling the keyboard, tape and TV display functions. The
latter is recognisable as the logic gate array (ULA) and the three
functional blocks
shown
in the
right
of the
diagram.
2.2 The
computer
is
built
on a
single
printed
circuit
board which
also
includes a regulated power supply fed from an external 9V power pack.
The keyboard matrix is part of the upper case assembly and is
connected to the board via two ribbon cables KB1 and KB2. A
description of each section follows.
1.1
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