Geoff Wearmouth

@warmtoffee.bsky.social

88 Followers 30 Following

Press plastic for a living but love the touch of rubber. Assembler of Gosh Wonderful and Looking Glass ZX Spectrum ROMs and my Binary Logic ZX81 ROM bl81.rom

A picture of ZX Spectrum and Jupiter Ace designers who were about to launch an inexpensive Forth computer. It will be manufactured close to where they live at Bury St. Edmunds east of Cambridge.
The cover of a ZX81 BASIC programming book designed by John Harris showing one of the jets that appears on top of the building on the Sinclair ZX81 manual.
Part of my first English language assembly listing to generate 16K ROM file for the 48K Spectrum which has been archived on the Wayback Machine since December 1998. There are two nice innovations (integer RND and integer TO_POWER) that Steven Vickers proposed for the Spectrum but it seems they were not allowed by the compatibility police. Most of the file, 90%, was written by myself. Some of my fixes appeared in magazines in the 1980s and, of course, I always contacted Sinclair Research and Amstrad first.
A simple recursive GOSUB test stops after twenty four attempts. ZX Spectrum about fourteen thousand.
Dr. Ian Logan after receiving an award for technical writing, mainly descriptions of the ZX80, ZX81 and ZX Spectrum ROMs.
The light colors computer with full memory was made by an uncle man and some student types way back then. With a single key it could accept do words and other presses made sense too. It was a good idea to save this stuff before running You could buy stuff to put in it though it took time. Crazy rock man or something. Break out was free. There was a write thing that worked with funny paper. There were only four lines of keys so simple. You had to join it to the tv to see stuff . They made a lot of them in black but only one white one. The uncle man got that one. I still have my first one and the do it this way book. Sigh.
Although labelled QL, this modem is for the ZX Spectrum.
A ZX Spectrum program that will run on a ZX81. I haven’t tried it. So busy. Use FAST command and save program and variables once complete. You can then print V$ at leisure. This is a spigot algorithm for PI which outputs 4 digits at a time. Original invented 1995. Only Sinclair computers could write strings longer than 255 digits back then. 🙂
The ZX Spectrum, launched in 1982, programmed by Steven Vickers who also wrote the manual.
ZX Spectrum with light grey keys and “issue one” printed on the circuit board
Lovely routine to print powers of two by splitting the internal number into two and recombining replacing missing leading zeros in the second segment.
The 1983 Microdrive Demo cartridges and use by Sinclair Research Limited. Written by Andrew Pennell.
A line number followed by a space is accepted and passed over in runtime.
This information should have been released by Sinclair Research back in 1985. Don’t put utilities in the former printer buffer.
ZX Spectrum math
This was once online. I may type it in for you. The code moved to Utility1 - a screen resident UDG and font editor which is downloadable and 128K compatible.
ZX Spectrum in production for 44 years and counting.
This ROM can be downloaded from spectrum.computing.co.uk and speccy4ever.
The cover of this well presented book gives a clue to the audience it is aiming at. Drawn by John Harris who drew the ZX81 manual cover it shows the same spaceship but this time in flight.
Andrew Pennel’s letter about Sinclair delays and pixels. He later crossed the pond to America where he wrote for Microsoft.
Ian Stewart is a lecturer in mathematics at Warwick University, the author of twenty books, including Concepts of Modern Mathematics, Get Knotted! and - jointly with Robin Jones - PEEK,POKE, BYTE and RAM - BASIC Programming for the ZX81.
ZX Spectrum power supply.
Sinclair 1983 ZX power supply. “MADE IN UK”. Those were the days.
Amstrad could not see what was wrong with this behaviour, which was not their fault and applied to all 128K BASIC implementations.
The addition of the three lines produces 1 2 3 And after a PAUSE and CLS 4 5 6
“Does he take sugar?” -tea lady.
I found this online. From 1973. Lovely code. I remain fascinated.
The slight alterations to the original program (posted by Eric Schraf on Facebook) enable the ZX Spectrum to store the output in a simple string. No 255 character restrictions on any ZX machine. This can be printed to the screen and the variable is saved when the program is saved. The BASIC starts slowly using two nested loops but quickens as the loops work downwards. Original BASIC runs on any computer with enough RAM e.g. ZX81, CPC464, C64 etc. This is now my favourite BASIC program.
A Few Moments Later… Rather slow but a fascinating PI Spigot Algorithm
Far from being unused, system variable 23681 is the high byte of PRCC so this moves the printer buffer down the screen 🙂
Celebrating a million Timex computers from Dundee -models ZX80, ZX81 and ZX Spectrum. All had forty keys only.
ZX81 App for iOS by Kevin Palser
A great analysis tool. Thanks
This is the Nine Tiles source code for the ZX Spectrum and the label for the first address is PLUGIN: ; HERE WHEN MACHINE IS TURNED ON
The image shows a listing of a program in the ZX Spectrum manual which accepts a date and returns the day of the week. I featured these lovely programs on my old demon website crediting Steven as author. I was delighted by my only contact with Steven which credited his mathematician/programmer turned mezzo-soprano sister with authorship. It is based on a program demonstrated to the press in 1950 and again in 1952. James Hardy Wilkinson demonstrated the machine explaining that an improved model The Deuce was being built by English Electric.
The image shows an assembler listing for a display function on the Sinclair QL or ZX Spectrum Next with a QL core. Also a BASIC loader if you can’t afford an assembler.
The fault appears with 10 INPUT #3; a$ (Missing hash) And prevents stream 1 being used in the standard ZX Spectrum. Steven Vickers states in the Pitman Pocket Guide that stream 0 is for INKEY$ and stream 1 for INPUT.
The very capable 8K ROM which was demonstrated at the Earl’s Court Computer Show was to be withdrawn for rewrite to accept the ZX printer.
The image shows a clean scan of the inside of the front cover which shows the author as Hugo Davenport.
A Coca Cola advert on top of a skyscraper in the artwork for the ZX Spectrum Introduction booklet by John Harris.
Since I started this thread I have found the ZX Spectrum source code on the Internet Archive. This is part of the LN routine. Steve used Clenshaw’s coefficients for SIN and ATN but his own for LN and EXP. This was written for the ZX81 of course. Would someone so gifted write the crass code that processes fractions? Worse still would they stick with it. Of course not.
I have fixed all three imperfections in my Looking Glass ZX Spectrum ROM. V1.08 So useful to enter the comma control by deleting the ink control code leaving chr$ 6. The magazine have got the third error wrong and the offending line is 10 INPUT #3; a$ I fixed this by calling CL_LOWER before selecting stream 1 at the start of INPUT which happily gets rid of the errant cursor. I had to check that to make sure. Ne ROM in the New Year.
A letter from Adam Hart-Davis who is 84!this year and developed and produced many computer and science series. He asks for computing celebrities and also developers of extraordinary uses for a forthcoming program “Me and My Micro”.
A very short but intriguing listing worth study. By G Bottomley. Page 33
Change txt suffix to asm. The sc01 files are a whimsy and not worth looking at. The disassembler in u3.asm is by John Kerr of Glasgow and was serialized in Personal Computer World. The sg81 source code can be read on the web page. Have fun.
The picture shows the recurring binaries that The Spectrum uses for the first digit after the decimal point. For the next and every digit there is a similar set of recurring binaries. The chances of these averaging out to the correct mantissa are surprisingly high - about 50%. Not good enough for collecting the 34th bit during division for instance. The author states in the source code that multiplication is adapted from the Zilog Developer Library. Not so the division as there is a bit missing in more than one way.
The ROM author mentions that he used CW Clenshaw’s Chebyshev coefficients for SIN and ATN but produced his own coefficients for LN and EXP. He had worked with Clenshaw and the coefficients were in his parent’s bookcase since 1954. They even credit his father in the front. He intended that he would implement digital to_power functions and also implement Newton roots - see back page. No point if he didn’t get rid of fuzzy logic first.
At the end of the ZX Spectrum ROM, Steven Vickers wrote to replace the small but slow TO_THE: routine with a fast accurate NEWTON-RAPHSON routine. Get my binary logic LOOKING GLASS ROM to experience this on a Spectrum (from speccy4ever and spectrumcomputing.co.uk)
This is the division routine from the ZX Spectrum source. The comments explain the process succinctly. The quotient may require a one shift left to normalize the mantissa in which case the 33rd bit in the accumulator becomes the 32nd bit of the mantissa and the 34th bit takes its place becoming the rounding bit. Because the ZX floating point machines use fuzzy logic and not binary logic to parse implementing this collection of the 34th bit would cause many errors.
Daily Mirror reporter Ruggles (one of three using this name) asks James H Wilkinson what happens when the Pilot Ace can’t do the task. He replies the computer makes anloud buzzing noise - like a Raspberry! (Note the reporter was accompanied by a photographer and back at base a cartoonist would draw the newspaper strip from what was recorded at NPL, BOAC etc. So for every sketch there is a high quality photograph. What an asset. )
The System Variable that controls the CYCLES OF ERROR NOISE has been named FART, later RASP, probably because when his parents took him to see what they had been working on he saw a computer that blew a Raspberry when there was an error.
The image shows a £15 thermal printer that uses an iOS app to print quality images from ZX81 and ZX Spectrum emulators running on Apple iPads and iPhones via bluetooth. There is a rechargeable battery inside the printer. Actually this printer comes with 14 rolls of paper and has its own character set for pdf documents and labels.
The Spectrum has the original ZX Spectrum keyboard but you can use a USB keyboard. A bargain
Completion of previous interrupt article and a ZX Spectrum Microdrive bootstrap program
A picture in case the link goes stale. Shown is the printer, which can be in the next room.
This bluetooth mini printer cost £15 and I have another that cost £8. I just use screen copies but proper integration would be nice. The ROMs would not require any alteration. The pictures show a moment from 3D Monster Maze and listings and images from my own utilities.
The peeker BASIC utility program shows three numbers. In the one letter at a time mode INPUT can be in lowercase. That is my preference. The square root of twenty five is a perfect five. Zero point five is perfect also, being a power of two, and the mantissa is thirty two zeros. On the original ZX Spectrum it was thirty one zeros followed by a one.
The 2002 custom ZX81 routine which was a translation of the FORTH routine in the Jupiter Ace manual. There are some of my superfluous instructions marked in red. The original ZX81 and ZX Spectrum routines get the square root of 25 slightly wrong. The C64 uses a similar, to power .5 , routine and gets the root of 9 slightly wrong. The routine shown is very accurate and gets the square of 64 and .25 correct on the first iteration. The routine shown is now widely used and features in RGL’s “The SPECTRUM”.