Z80 Computer

24032011399-200x200This is a project I made a some years ago, a Z80 computer system. The “core” is functional, however, due to the lack of free time, other projects, and the old source code that I don’t seem to find anymore (must search old backups), some features are not yet functional and I don’t know when they will be. What is not working: VGA output, RTC, SD CARD, PS/2.

Firstly, I would like to say thanks to Thomas Scherrer, from http://z80.info/ . A great site with a lot of great info about Z80 systems, code, schematics, datasheets and so on. You can basically have no ideea about what a Z80 CPU is, and make a functional system (HW and SW) just by reading what’s on z80.info .

A small description of the system:

-Z84 CPU clocked at 3.57MHz , with a secondary oscillator to overclock the CPU to 8MHz (and yes, it works)
-32KB of ROM memory, 27C512 EPROM, half used
-32KB of RAM memory, M48Z25-70, Zero Power RAM, with internal Lithium battery
-2×16 LCD with backlight, HD44780 compatible controller (KS0066)
-6 8bit parallel ports, by using two 82C55 Programmable Peripheral Interface chips
-RS232, by using 16C550 UART + MAX232 level shifter
-RTC 72421 with battery back-up
-ISA port for ISA Video CARD. Missing “glue” logic.

This is how it all started, a test PCB, one Z84 CPU (the big one on the left), one 62c256 32KB RAM, one 27C512 64KB EPROM and some glue logic:

Selection_053

Some pictures during the construction:

10012005

09012005(017)

09012005(014)

09012005(013)

The inductor under the LCD is for a 5V switching mode power supply, used for the LCD backlight. The LCD that I used in this system wants a LOT of power for the backlight, it was killing the main linear regulator (the 7805 upper right, with a radiator attached).
09012005(012)

09012005(010)

09012005(009)

09012005(007)

A lot of wires on the back:
11012005(002)

And the first thing displayed, “Hello World”. It actually didn’t work on the first try, since I accidentally inverted all the LCD data lines.
11012005(001)

More wires:
P1020518

P1020524

ISA card mounted on extension board:
P1020527

P1020533

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The first two boards (pictures are a little old, the final version has 4 PCBs, and it’s also battery powered by using LiPo cells):
P1020535

P1020536

P1020537

Boards stacked and powered up:
24032011399

Selection_054

The schematic:

schematic_1

Schematic in Eagle format can be found at:
www.hackingbeaver.com/z80_computer/z80_computer_schematic.sch

Some useful datasheets:
www.hackingbeaver.com/z80_computer/z80cpu_um.pdf
www.hackingbeaver.com/z80_computer/16c550.pdf
www.hackingbeaver.com/z80_computer/27c512.pdf
www.hackingbeaver.com/z80_computer/62256.pdf
www.hackingbeaver.com/z80_computer/82C55DL.PDF

Updates to come!

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