This is what my home made computers are based on, except i built mine on vero board, and added extra hardware and increased clock speed.

I discovered the awesome microprofessor - MPF1B way back in 1990 when i was doing an btec electronics engineering course. I used them in the parts of the digital electronics and microprocessors sections of the course. I had a maplin z80 cpu board with a monitor program and keyboard for entering instructions but its design was nowhere nears as good as the MPF1B.

For a start the Microprofessor - MPF1B had the ability to save and load your programs to a cassette tape. Its monitor program allowed you to single step through your program and look at the cpu registers. It allowed you to set a breakpoint in your program so that it stopped at a point you wanted. It had some basic editing features like copying code blocks to different place in memory and an insert and delete commands. It had a relative jump calculation command. And it had amazingly a BASIC interpreter as well. It came with a parralle port and a counter timer too. You had to get used to using a six digit led display.

Of course now i new i had to have one of these. So i built my own on veroboard. I got a copy of the ROM so it was essentialy the same thing except i didnt add the parralle port or the counter/timer. I added an expansion connector to it. I used to have great 'birds nests' of wires every where and different boards for different circuits. My first attempt at building an MPF1B worked well enough except the connectors wernt very reliable. So i built another version of this computer and added the parralle port and counter time this time. By now i was getting really quite good at writing low level machine code programs. About 1993 i decided to sell my first version of the mpf1b to an engineer who worked at Nokia where i also worked at the time. It was to recoup some cash to build an even bigger better computer.

The bigger better version of the MPF1B or as i now called it, UPF-1D had the same OS. Running a monitor and with the same BASIC as the original. Buy that time i had developed an interest in digital music and synths so that was gonna be a major feature of this machine. The ram on earlier versions was only 8Kb so i new i need much much more ram. I added many extra hardware features to the design. I built it with the very highest quality parts i could buy too which is why its still running to this very day.

The design took shape. To satisfy my interest in electronic music i added a MIDI interface which has a 6850 serial interface chip and the associated circuitry to convert to the midi standard for keyboards etc. Next i added an 8 bit digital to an*louge converter and an 8bit an*louge to digital converter. This is to allow me to record and play sound and generate waveforms etc. Then to satisfy my need for more memory i gave it 128Kb of ram. I designed the ram to be paged as 16 blocks of 8Kb so that i didnt have to design extra address decoding. It meant if i added more ram later the page would become 16 blocks of 16kb and that meant almost a 1Mb of memory was possible fully expanded. I added a real time clock to enable timing events to be handled accuratley and i even wrote a digital clock software too. Then i also added the Z80PIO parrelle interface chip and the Z80CTC counter time chip to finish it off.

In 1994 i left Nokia and moved from Surrey to East Suss*x to do a Higher National Diploma (HND) in electronics at Hastings College and Brighton university. The new computer project was built and running within 3 months with the exception of the bits handling the audio inputs and outputs to the converters. The wires to them were just attached to tempoary wires. Now it meant i could write software to record and play back sounds and trigger them from a midi keyboard. The sound quality wasnt fantastic but it was the fact it could be done and the satisfaction. I wrote lots of software with this machine and i would also get the previous computer i built to link up with it. I built a midi interface and an rs232 serial interface on seperate boards for the older machine.

After i finished my HND course and got a job i set to building some an*louge filters and a little mixer to finish the new computer of. The filters helped roll off high freguencys that were too high for the sample rate i could make the system work at. The maximum sample rate was about 16Khz which gave about 8 seconds of record time. The mixer is to feed back a portion of the output audio signal to the input. This allowed me to create delay, chorus and r type sound effects to process the audio signal. This is how my music carreer started. I still use my computers to this very day some 13 or years on and hopefully into the future. Have a read about my not so successfull quad processor z180 system in my other post - z80/z180 based systems.