1.3 MEMORY
The
Z80
microprocessor can directly access any location in a 64 KB
memory block.
In order to have a maximum flexibility for applications, the
CoBra
microcomputer is bundled with the maximum
RAM
memory that can be
accessed by the microprocessor, i.e. 64 KB. At power-up, the
RAM
memory has a
random contents. Therefore the existence of a non-volatile memory is needed,
one that wouldn't lose its contents at power-off (
EPROM
). The
CoBra
computer
can be equipped with 2 to 16 KB of such a memory, the standard version
having 2 KB.
In this memory there are recorded power-up specific programs, such as
hardware tests, a test image used for adjusting the black & white or color
monitor, computer configuration user selection indicating the source of the
operating system to be loaded:
—
BASIC
interpreter – Sinclair ZX-Spectrum compatible, with a
monitor program for work in assembler and with printing routines
specific for
RS-232
serial interface printers;
— Sinclair ZX-Spectrum
BASIC
interpreter, unmodified, for
applications that verify the genuineness of the existing ROM;
— operating system specialized in assembler work, with editor,
assembler, disassembler, copier (ex.
OPUS
);
— any other user-designed interpreter. (ex.
FORTH
);
—
CP/M
compatible floppy disk operating system.
Spectrum-type operating system can be loaded from 16 KB
EPROM
memories, from magnetic tape or disk.
The
CP/M
operating system can only be loaded from disk, its operation
involving the existence of the floppy disk.
On one hand, the Sinclair-Spectrum compatibility requires that the
RAM
memory between addresses
4000H
and
5AFFH
contain the information used by
the video controller to display a 256x192 pixel image on the monitor, on the
other hand running the
CP/M
operating system becomes impossible if the video
memory shows up in the middle of the transient program area (
TPA
).
In order to solve this problem created by the dual nature of the
computer, a memory configuration and selection circuit was created that
satisfies the conditions imposed by these three configurations. This circuit is
made of two D-type flip-flops (
U36
), a BCD-to-decimal decoder (
U56
) and gates,
being presented in the block diagram in
Fig.2
.
The main advantage of this circuit is that it allows switching the memory
configuration with a jump anywhere in the 64 KB space of the new
configuration, even if the memory area containing the switching routine
dissapears as a result of the switching.
8
Содержание CoBra
Страница 20: ...Fig 10 Keyboard schematic 20 ...
Страница 21: ...Fig 11 Keyboard schematic 21 ...
Страница 23: ...Fig 13 Power source schematic 23 ...
Страница 39: ...9 APPENDIX 1 CoBra Microcomputer Schematics 39 ...
Страница 40: ...Fig A1 1 CoBra Microcomputer Central Processing Unit 40 ...
Страница 41: ...Fig A1 2 CoBra Microcomputer Configurator and Selector Circuit 41 ...
Страница 42: ...Fig A1 3 CoBra Microcomputer Read Only Memory Circuit 42 ...
Страница 43: ...Fig A1 4 CoBra Microcomputer DRAM Memory Circuit 43 ...
Страница 44: ...Fig A1 5 CoBra Microcomputer Memory Access Prioritizer and Command Logic 44 ...
Страница 45: ...Fig A1 6 CoBra Microcomputer Video Address Generator Circuit 45 ...
Страница 46: ...Fig A1 7 CoBra Microcomputer Video Address Multiplexer Circuit 46 ...
Страница 47: ...Fig A1 8 CoBra Microcomputer Video Memory Circuit 47 ...
Страница 48: ...Fig A1 9 CoBra Microcomputer Video Sync Pulses Generator Circuit 48 ...
Страница 49: ...Fig A1 10 CoBra Microcomputer Video Signal Shape Generator 49 ...
Страница 50: ...Fig A1 11 CoBra Microcomputer Interfaces 50 ...
Страница 51: ...Fig A1 12 CoBra Microcomputer Voltage Level Adapter Circuits 51 ...
Страница 52: ...Fig A1 13 CoBra Microcomputer Keyboard Interfacing Circuit 52 ...
Страница 53: ...Fig A1 14 CoBra Microcomputer TV Monitor Interfacing Circuit 53 ...
Страница 55: ...10 APPENDIX 2 Flopppy Disk Interface Schematics 55 ...
Страница 56: ...Fig A2 1 Floppy Disk Interface Disk Controller 56 ...
Страница 57: ...Fig A2 2 Floppy Disk Interface Command and Control Signals Generator Circuits 57 ...
Страница 58: ...Fig A2 3 Floppy Disk Interface Write Clock and Digital PLL Circuits 58 ...
Страница 59: ...10 APPENDIX 3 Component Placement on Boards 59 ...
Страница 60: ...60 Fig A3 1 Component Placement on Keyboard Circuit Board ...
Страница 61: ...61 Fig A3 3 Keyboard Circuit Board top layer seen from above keys side ...
Страница 62: ...62 Fig A3 3 Keyboard Circuit Board bottom layer seen from above keys side ...
Страница 63: ...Fig A3 5 Component placement on the floppy interface board 63 ...
