Z80 Single Board Computer

This is my first didactic 8bit – Z80 based computer.

I’ve made it because I was interested into homebrew a working computer from TTL chips since high-scool times. I was intrigued by the idea of better understanding of PC architecture and  I wish to learn programming with assembler language.

My project starts copying Grant Searle’s project: Grant’s 7 chip Z80 Computer

Original schematic by Grant Searle

Please note that I’ve changed the way of the UART/RS232 converter is wired. In fact I’ve lost a lot of time following Grant’s schematic: everything double cecked but no data received to the serial port… uhm… I’ve solved in this way:

No jumpers between DB9 connector pins or other RTS shit… just a simple straight RX-TX converter between 6850 UART and DB9 connector.

I’ve build it using point-to-point wire soldering on a veroboard prototyping board. At the moment it comunicate with me via a RS232 serial link.

The schematic is the same of the Searle’s website except I’ve modified the clock source and the init.asm code that drive the 68B50 ACIA.

I’m using a 1.8432Mhz crystal oscillator at first for cpu and ACIA then switched to drive the cpu via a 10.240Mhz crystal oscillator. The 1.8432Mhz crystall only drive the ACIA… setting the divider byte to 16 generates 115200bps.

Z80 SBC connections details
Z80 SBC solder side details

I’ve benchmarked it’s performance via the Mandelbrot generator provided by the RC2014 project.

color_mandelbrot    mandelbrot

This RC2014 project started years ago like mine copying the Searle’s project and improving it so it’s 100% compatible with mine.

The results? At 1.832Mhz it took 46:52 Minutes to complete. At 10.240Mhz just 8:31 minutes

Here you can find the complete MS Basic language reference Microsoft_Basic_8086Xenix_Reference

And here the Nascom Basic NASCOM_Basic_Manual



Author: l.i.papadopol