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CMOS Logic Computer

8-bit CMOS Logic Computer

This is my 8-bit computer built from CMOS logic gates, based on the SAP-1 in Albert Paul Malvino’s Digital Computer Electronics. It was hard to avoid creating a rats’ nest of wires, but there is (surprisingly) about 40m of wire in total. Its hard to gauge the amount of detail to describe this project in; there’s enough for a whole book’s worth describing it from the logic gates up, so I’ve provided a brief overview and a video that shows how it works in action!

The computer is fully programmable and it can add and subtract numbers from 0 to 255. The computer is organised around an 8-bit parallel data bus. At its heart is the adder/subtracter, which performs the computer’s calculations, either side is a register, which together hold the two numbers to be added or subtracted. Once the calculation has taken place, the result is stored in the upper register, which is called the accumulator. The result can then be sent to the output register, which drives the 8-bit LED display, or further operations can take place.

CMOS Logic Computer
CMOS Logic Computer

Data and instructions are stored in the RAM, which is the most complex chip on the computer. Two chips of 16 4-bit words each combine to make one 8-bit word; giving the computer a total memory of 16 bytes.

A 555 timer divided by a flip-flop provides the clock and drives two counters. First, the program counter, which is used for loading instructions,  and second the ring counter, which generates T states for the control logic, which is made entirely of NAND gates and inverters.

The two most complex chips are the RAM and the 4-bit adder, all of the other components are Logic Gates or Flip-flops. Incidentally, these are the only TTL chips on the computer as they were not available as CMOS. Their inclusion has taught me the practicalities of level shifting.

Whilst the computer’s functions are basic, building it has taught me the fundamentals of digital logic and computer architecture. Also, reading how these work in a book is very different from making them a practical reality.


The computer has 5 instructions:

LDA 0000 +4 bit address  which loads a number into the accumulator, this must be the first command.

ADD 0001+4 bit address adds a number at a 4-bit address to the accumulator.

 SUB 0010+4 bit address subtracts adds a number at a 4-bit address to the accumulator.

 OUT 1110 XXXX outputs the accumulator value to the display

 HLT 1111 XXXX stops the computer’s clock. All programs must end with this instruction.

These instructions are loaded into the upper nibble (4-bits) of the computers memory and where an address is needed it is added to the lower nibble. The program counter starts at 0000 and continues counting upwards to 1111 unless a HLT instruction is received, so numbers to be added or subtracted have to be entered in memory locations after the HLT. This is shown in my video, where I write a program to do the sum 63 + 111 – 56 = ?

The program is as follows:


0000 00000101 @Load Value at address 5 into the accumulator

0001 00010110 @Add Value at address 6 to the accumulator

0010 00100111 @Subtract Value at address 7 from the accumulator

0011 1110XXXX @Output result to LED display

0100 1111XXXX @Stop the computer

0101 00111111 @63 in binary

0110 01101111 @111 in binary

0111 00111000 @56 in binary

Output = 01110110 in binary or 118



Reappraising the Seicento

‘Reappraising the Seicento’ Available Now

It is now possible to place an order for my book ‘Reappraising the Seicento: Composition, Dissemination, Asslimilation’ of which I am both a joint editor and contributor.

Reappraising the Seicento

Reappraising the seicento presents new perspectives on some relatively well-researched areas of music history and adumbrates some more arcane aspects of the period, offered by fledgling scholars and early career researchers in the field of musicology. The scope of the title has the potential to warrant a tome on the subject, but it is not the intention to provide a comprehensive survey of music in the seventeenth century. Instead, five essays are presented, divided into two sections, which represent the research activities of young scholars with an interest in the seicento.

In the first part of this book compositional procedure in seicento Italy is examined through two different analytical procedures. Musical styles and fashions changed considerably throughout Europe in the seventeenth century; at the forefront of these changes were Italian composers and performers, who found fame and influence in their native countries as well as abroad.

In the second part of this book the dissemination of Italian music in seventeenth-century England and the appropriation and assimilation of contemporary Italian compositional techniques by English composers are considered. The phenomenal interest shown in Italian music by English patrons and musicians of the seventeenth century is placed into context and is revealed to be part of a larger historical trend.

It is available on amazon.co.uk via this link: http://www.amazon.co.uk/dp/1443855294/

Don Carlo Gesualdo

A Jargon Free Explanation of my PhD Research

Don Carlo Gesualdo was an Italian Prince in the Renaissance. He was born into one of the richest families in Naples and married the most beautiful woman in the south of Italy. Unlike most aristocrats of his day, he was a virtuoso musician and composed beautiful and expressive music, but there was also a darker side to his character. Catching his wife and her lover red-handed, he brutally murdered them both before fleeing to his hilltop castle. There, in the courtyard, he had his youngest son whose parentage he now doubted, rocked to death whilst a choir sang songs about death.

Travelling across Italy to Ferrara he encountered many new musical experiences and married again. He took his new wife back to his castle where a long abusive relationship was about to begin. Five years later, his mistress was tried for witchcraft. After being tortured, she confessed to poisoning the Prince, in quite disgusting ways, so that he would fall in love with her. She was locked up in the castle dungeon.

Isolated from society, Gesualdo occupied himself with hunting and music. During his later life he developed masochistic tendencies and employed servants to beat him. Eventually, after the tragic death of his son in a freak riding accident, he locked himself in his music room, where he would spend the remainder of his life.

Gesualdo’s own distinct personality found its way into his music and this makes it very exciting to study. His was extremely innovative and he wrote harmonies that would not be heard again for three hundred and fifty years. What makes this so interesting is that the music was written before we had our system of scales that we use today and call ‘The Tonal System’ but was written using earlier music theory the ‘Modal System’. This system did not develop in such a way that it can explain how Gesualdo’s music works and this is what my research sets out to do.

Understanding how music was written and how people react to it is crucial for society. Everybody reacts to music, however diverse the reactions may be, and Gesualdo always provokes a response. Unravelling the creative processes behind his compositions is crucial for creating new music and throughout the last century many composers have found inspiration in the Prince’s works. Not only does his life make the plot of a good opera, there have been ten so far, but his forward looking nature provides inspiration for the generation of new music. In fact, I began studying Gesualdo as a composer.

Gesualdo’s life and music are both extreme. They continue to drive new composition and research. Taking the music to pieces to see how it was made is an integral process in understanding how his music reacts with society. When it is as radical as Gesualdo’s, this relationship becomes even more exciting and is the motivation for my research.

For more information, visit http://www.gesualdo.co.uk or e-mail me a question!