Zx spectrum ula reverse engineering The revised clock generation is shown in the clock and horizontal control schematics There are two separately occasions when the ULA generates RAS and CAS signals: once for ULA video access to the lower 16K, and the other when the CPU requires access. As discussed previously, the Spectrum ULA applies a special contention pattern to the second T-state (T 2) of an IO instruction. An analysis of the floating bus values returned whilst reading port 0x40FF reveals that the second attribute byte fetch only is returned - the timing of which are altered due to the applied contention. The CPLD implementation inverts its 3. If however the Z80 takes 3 cycles to acknowledge the interrupt, then we would loose 3 T-states between the interrupt generation and the first contended cycle, making the above table start at 14333, and the first contended cycle at 14335 - exactly as the FAQ and test programs report. Share. Jul 30, 2010 · A site dedicated to the reverse engineering of the ZX Spectrum and related projects. Once proof copies have been checked, distribution will begin! Read More This table assumes that the Z80 responds to the interrupt immediately, which cannot be the case. This pattern is different to that used to avoid video memory contention. The contended floating bus read (say port 16639) does not return the usual 67, 255 x 7, 69, 255 x 7, 71 sequence but instead returns 67 x 8, 69 x 8, 71 x 8, etc ( where The display was identical to a real ZX Spectrum issue 3 I had connected to the TV at the same time, for reference. A +D disk containing the original cassette master maker for my unpublished game Skyway has been found, and uploaded to the ZXDesign website! Documenting the reverse engineering of the ZX Spectrum ULA; The ZX Spectrum ULA book; creation of a 100% compatible clone and next generation implementations, and new ZX Spectrum software Feb 7, 2010 · If this is wrong, then the clock will be held low during ULA video memory access instead of high. For this to occur, state T 3 of the IO instruction must complete during cycle 7 or 8 of the ULA's 8 cycle wide period. The Sinclair ZX Spectrum ULA Book The ZX Spectrum Reverse Engineering and Clone Desgin Blog Feb 17, 2010 · The Harlequin boots okay, but the first video byte during uncontended floating bus read is returned at T-state 14343, which is four T-states earlier than a real ZX Spectrum. Once proof copies have been checked, distribution will begin! Read More So this site is dedicated to the design of a ZX Spectrum Clone. Internally these are treated as 8 half-rows of 5 keys. The ZX Spectrum is clocked at 3. The keyboard is read by reading from port 0xFE - however the upper eight address lines play a role in determining which half row is to be read. co. Once proof copies have been checked, distribution will begin! Read More May 22, 2022 · Reverse Engineering a ZX Spectrum Keyboard Last time I looked at the many variations of the 40 key 8x5 matrix keyboard found on many 1980's home computers. ZX Spectrum design bugs such as "The Snow Effect" Hidden features of the ZX Spectrum; ULA version differences; Read the fantastic reviews on . ULAs were used extensively in the ZX80, ZX81 and the Spectrum due primarily to Clive Sinclair's obsession with miniaturization (at a low, low cost). What ULA works in what machine? The 6C001E-7 ULA is backwards compatible with every 48K machine from the Issue 1 right up to the Issue 6A. The book is the result of opening the chip and reverse-engineering it down to the transistor level. The Spectrum ULA stops clocking the CPU with CLK held high whenever it needs access to the video memory at the same time as the CPU. This book is super nerdy, it covers the design of the ULA chip that was a core chip that was in the specie, the ULA was a custom chip that was responsible for tieing the various other chips inside the spectrum together, it was the bit that made the spectrum, well, the spectrum. As part of the on-going Harlequin design I've been looking at what would be required to implement a ULA replacement for a standard ZX Spectrum 48K. 5MHz CPU clock output, as the ZX Spectrum will invert it back to its proper phase with a transistor driver before passing it to the Z80. First a summary. Please support the research, reverse-engineering and writing effort that went into producing this book, by buying directly from the ZX Design website. The original Spectrum keyboard is of course a style icon, but it wasn't great if you were doing lots of typing. Aug 29, 2012 · These guys have managed to completely reverse engineer the Sinclair ZX Spectrum, including the ULA. A single ZX Spectrum display row takes 224 T-States, including the horizontal flyback. During a ULA IO port access the IO instruction must request data from or send data to the ULA when the ULA is not busy updating the display. This is a very simple and clever way of pausing the CPU, and Sinclair presumably implemented it like this to avoid dedicating a valuable ULA pin to the job of controlling the CPU WAIT signal. The fact that the first offest between floating bus reads is 2 must have something to do with the way Floatspy implements it's timing, and must be subject to the effects of memory contention. Jul 30, 2010 · Some of the topics covered are: The architecture of the standard microcomputer, Ferranti and their ULA, manufacturing process and structure, The functional layout of the ZX Spectrum ULA, Video display generation, Memory contention and timing, ZX Spectrum design bugs such as "The Snow Effect", Hidden features, ULA version differences. For every T-State 2 pixels are written to the display, so 128 T-States pass for the 256 pixels in a display row. At the end of it we may even get a working ZX Spectrum clone Dec 6, 2016 · The British ZX Spectrum computer had many clones in the Eastern Bloc. uk. The writing and production of The ZX Spectrum ULA: How to design a microcomputer has been completed and the book is with the printer. "The ZX Spectrum ULA: How to design a microcomputer" is pitched to be readable by the novice, but quickly moves into more complicated territory, and would be readable by anyone with a general interest who can follow boolean logic, the electronics hobbyist, the electronic engineering student, retro-hardware fan or just a piece of shelf-candy for The writing and production of The ZX Spectrum ULA: How to design a microcomputer has been completed and the book is with the printer. Based on Chris Smith's excellent book 'The ZX Spectrum ULA: How to Design a Microcomputer' which documents reverse engineering the Ferranti ULA within the Spectrum. For other ULA revisions, the following holds: 5C102E – Issue 1 and 2 PCB’s (requires cockroach mod). Jul 29, 2010 · If you grew up in the British 80's, you probably either had or knew somebody that had the ZX spectrum. May 24, 2020 · A few years ago Chris Smith reverse engineered the ULA and wrote a book about it. This was the first 100% compatible reverse engineering of the ULA making it possible to replicate the ULA with standard components. When the ULA is updating the display and needs to access the lower 16K of memory it generates a RAS and CAS sequence synchronised with its display byte fetch. The ULA was a . Which is exactly the offset sequence shown by a ZX Spectrum, but one T-state early as the Spectrum begins at 14344. The revisions to the Clock, cpuControl and waitGen schematics may be found in the schematics version 1. Buy, and study carefully, The ZX Spectrum ULA. 5 MHz, so if 2 pixels are written in a single CPU clock cycle, the pixel clock of our display must be 7 MHz. In true research lab fashion this site will document the complete progress: the questions, the answers, the mistakes and the eureka moments. The missing functionality is that of the analogue sections, notably the cassette interface and video output. ULA Video Access. How were these chips made? In fact, referring to the ZX Spectrum schematics shows Sinclair using 8K2 resistors for the databus pull-up. These all worked as intended which is good news, confirming that the CPLD implementation and its dynamic RAM interface demonstrates a true 48K ZX Spectrum ULA behaviour. Nov 26, 2016 · The Harlequin is a clone of the ZX Spectrum using standard TTL parts. Feb 7, 2010 · The ZX Spectrum ULA has been reverse engineered into full schematics, which are being analysed and written up into The Sinclair ZX Spectrum ULA book. One of the main differences in the Harlequin design is the lack of dynamic memory interface. 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. 16 . This proves that the Harlequin does indeed reproduce the ZX Spectrum timings - an excellent result as we're considering a ULA replacement. The Russian Wikipedia mentions the КР1858ВМ3 which is a Z80 clone, and the Т34ВГ1, which is the same thing as a ZX Spectrum ULA. The ZX Spectrum keyboard consists of 40 keys arranged as 4 rows of 10. It seems many of them were built using Russian-made chips from the Angstrem factory in Zelenograd in/near Moscow. The ULA handles its IO port separately to the video, however it has a single data bus and so cannot perform both tasks at the same time. drkglml mtcc wqkdcp akkqt zcwrzm oxda koqsy ubzdhmsh yyoyk xhwjj