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Inside the Ferranti ULA
Dec 19, 2008
A vast amount of research has been carried out over the last six months into Ferranti, their ULA technology and fabrication, the Spectrum ULA design and the differences between the 5C and 6C ULA's.
It has been a fascinating journey of discovery!
Overall it has been extremely difficult to obtain information on the ULA. After many months of searching for the Ferranti ULA Technical Handbook, Paul Hartley came across my information request on a datasheet forum and kindly sent me his copy! This contains plenty of specification details on the 1000, 2000 and 5000 RTL and CML series ULA's but lacks quite a lot of essential detail, such as the structure of the ULA peripheral cells.
I have combed the libraries, and bought several excellent books for the odd paragraph on the ULA they contain, and extracted snippets of information from a small selection of papers and on-line references.
On top of the academic research, a great deal of non-invasive reverse engineering and analysis has been carried out on the Sinclair ULA, including dynamic response approaches like ramping the clocks up and down to see which ULA generated signals are propagation delayed and which are clock synced. This proved useful and gave clues as to the implemention of the now know functionality, particularly the RAS and CAS generation.
In October a thread of investigation led me to the Manchester Museum Of Science and Industry, and I discovered they hold the Ferranti archive. This archive had only recently been added to the National Archives website, and it was by pure chance that I came across it. I immediately contacted the MOSI and arranged a visit to review any ULA information they held, and many thanks to Jan Shearsmith the archivist for his kind assistance. The archive contains mostly marketing and publicity but sadly little technical information. There is a technical product brief for the 'R' series ULA, which followed the 1000, 2000 and 5000 series CML ULA's and was available in the early 1980's around the time of the ZX Spectrum. This provides some useful clues as to the makeup of the 5000 series peripheral cells, and perhaps the 6000 series itself, however the 'R' series ULA is a very different structure to the earlier CML series.
Interestingly, and frustratingly, there are no references to the 6000 series ULA that would have been the basis for the Sinclair 6C001E ULA, even in product selection guides from the mid 1980's that make comparisons with the earlier ULA types.
In spite of these difficulties, a great advance has been made recently. Mike Connors at Raw Science (a division of Datel) has very kindly assisted me with the decapsulation of the 6C001E-7 ULA (pictures below). This took several devices, so I have a few broken machines in need of replacements.
I am meticulously back-annotating the resulting images into a schematic, which in it's native transistor form will measure more than 168 x 178 cm.
The following images are a taster of what's under the ULA hood...
X-Ray of ULA and photo of die
Photo of die identifier