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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 30th Jul 2021, 1:41 pm   #1
Timbucus
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Default Early use of ULA's

As there are so many knowledgeable people on here I wonder if anyone has any memories of where they first saw a ULA in use. It's use in the ZX81 to reduce the chip count from the ZX80 seems to be the first use in a computer I am aware of and maybe Clive became aware of the technology as the NEB had a large stake in Ferranti in the mid 70's. The fact this lead was abandoned means often the ULA isn't even in the list of programmable chips mentioning PAL,GAL,ASIC,FPGA etc.
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Old 30th Jul 2021, 2:36 pm   #2
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Default Re: Early use of ULA's

80s era home computers were my first experience of them, specifically the ZX81. I believe there is a book which focuses on the sole subject of the ZX Spectrum ULA.
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Old 30th Jul 2021, 3:16 pm   #3
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Default Re: Early use of ULA's

..And here it is. I have not had the opportunity to read it myself.

https://www.amazon.co.uk/ZX-Spectrum.../dp/0956507107
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Old 30th Jul 2021, 5:54 pm   #4
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Default Re: Early use of ULA's

I recommend it - a brilliant book. I actually went to a BCS lecture in Cardiff by Chris Smith many years ago where he had his breadboard Spectrum (2012 I think) I dragged my son along and he was not totally bored...

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As you say most people you speak to seem have first seen the technology in the ZX81 but, that cannot have been its first use - it was developed late 70's by Ferranti and then just dropped as a technology in the late 80's I believe.
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Old 30th Jul 2021, 7:00 pm   #5
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Default Re: Early use of ULA's

My first employer customised a Ferranti ULA for CAMAC modules.
https://en.wikipedia.org/wiki/Comput...nt_and_Control

The Ferranti ULA was expensive in the relatively small quantities needed, especially if the mask design was not correct first time. By 1975 the expanding range of standard ICs such as the SN74125N (quadruple bus buffers with 3-state outputs) were lower cost and more flexible for new designs than the Ferranti ULA.

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Old 3rd Aug 2021, 12:01 am   #6
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Default Re: Early use of ULA's

Even "ASIC" covers a lot of ground. The important thing is: how many of the masks needed to make the chip are special to MY product and how many of them are shared by ALL products. As a general rule, the lower masks (eg to define implants) are finer geometry and more expensive and the upper masks (eg to define metal interconnect) are coarser geometry and less expensive.

Today, ASIC tends to mean a device for which ALL of the masks are specific to the design. A mask set can cost $1,000,000. If you are "lucky" design mistake(s) can be rectified by a change to the metal masks alone (the digital circuitry can include a scattering of "spare gates" that can be deployed to make circuit changes).

Historically, ASIC included such technologies as Sea Of Gates (SOG). With SOG, the vendor would have a set of die sizes with I/O cells on the periphery and low-level transistor array throughout the rest of the die area. The masks used to create these base layers would be common to all designs. A customer's design would define the upper layer metal masks, which would configure the transistors into gates and the gates into functions -- and configure the I/O cells appropriately. There might also be some specialised routing resource for clock trees.

The next step after this (I think LSI logic called it a "masterslice") would include a mix of SOG and some specialised functions -- like a simple processor, or some RAM blocks, or a PLL.

These "old style" SOG devices have got a lot in common with today's FPGA devices; where SOG parts were configured by (expensive-ish) metal masks, FPGAs are configured by RAM cells.

I believe that the ULA was a somewhat older/cruder version of the SOG-style of device that I described.

The ZX81 was probably the first/most famous ULA consumer, but I thought that the custom chip in a BBC micro was also a ULA (that caused a lot of trouble due to problems with the internal clock distribution). I wonder whether the Elan/Enterprise chips were ULAs (wikipedia doesn't tell me and I've never seen inside one. I do remember being at the PCW show the year it was launched, and admiring its sleek case, but was then thrown off the stand when one of my friends spotted that the box only contained the keyboard and that all the hard work was being done by a large discrete-chipped prototype behind the curtain)

AFAIK, the PLA pre-dated the PAL. The PAL was a wonderful invention and MMI had the most fabulous data-books that were not only clear and concise but contained amusing cartoons. When AMD bought MMI the cartoons were slowly phased out (Boo!)

The Soul Of A New Machine (Tracer KIDDER) describes, in part, how the PAL was instrumental in allowing Data-General to build their 32-bit "VAX Killer" for less money and on fewer boards.

Neal.
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Old 3rd Aug 2021, 1:31 am   #7
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Default Re: Early use of ULA's

AMD did some 'bit slice' CPUs like their 2901, where you built up as many in parallel as you needed to suit the word width you required. They weren't in any way hard programmed. Their schtick was that they were fast. Some of them were used in our early DSP boxes.

PLDs of that era were combinatorial logic trees into output pins, with or without flip flop registers fror the pins. A typical part of that period was the 16R4. 16 input pins into four combinatorial trees into four flip flops into four outputs. Just enough to do a four bit counter so definitely MSI at most. But with care and a suitable application, you could sometimes make them do more if you were artful. Early PLDs were at the power hungry and fairly quick end of the spectrum.

I remember Ferranti visiting and putting on a presentation, hoping to flog us ULAs. They were talking of devices substantially larger than PLDs were then, but also substantially slower. The speed was the killer for us. We needed things for the data rates of the day and this wasn't negotiable.

Many years later, I was designing with Altera 10k family PLDs with 4700 logic cells and rated by the manufacturer in the 100,000 gate equivalent. I had a custom DSP engine built with a array 24bit*24bit multipliers and a big integrator. Good fun at the time!

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Old 3rd Aug 2021, 9:22 am   #8
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Default Re: Early use of ULA's

Quote:
Originally Posted by NealCrook View Post
The ZX81 was probably the first/most famous ULA consumer, but I thought that the custom chip in a BBC micro was also a ULA (that caused a lot of trouble due to problems with the internal clock distribution)
The original BBC Micro contains two ULAs. The Video ULA does clock division, palette lookup and contains the shift registers for pixel output. The Serial ULA also does clock division, some routing and a bunch of stuff for the cassette interface (carrier detection and demodulation, I think).

The early ULAs were Ferranti parts but the supplier changed to VLSI Technology later. The later devices run cooler. I don't know what architecture they have inside - whether they're still strictly ULAs or reimplementations of the same logic as an ASIC.

The later Master machines contain more custom chips which I think also came from VLSI Technology.

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Old 3rd Aug 2021, 9:56 am   #9
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Default Re: Early use of ULA's

Quote:
Originally Posted by cmjones01 View Post
The early ULAs were Ferranti parts but the supplier changed to VLSI Technology later. The later devices run cooler. I don't know what architecture they have inside - whether they're still strictly ULAs or reimplementations of the same logic as an ASIC.
The Ferranti ULAs were bipolar using a simple CDI process with about 5 masks, which was the same as old metal-gate PMOS. So it was a cheap process to make. The disadvantage was that being bipolar, it hoovered up power.

VLSI Technology by the early 80's had a good 2um CMOS process (I recall visiting their fab in Santa Clara in 1985 or thereabouts) which allowed them to make fast, low power gate arrays (gate arrays and ULAs were basically the same - a regular array of logic gates, with the metal interconnect customised for each end user design. That made them cheaper to produce than ASICs, where all the mask layers were customised for the design). But they also made ASICs too.
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Old 3rd Aug 2021, 11:06 am   #10
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Default Re: Early use of ULA's

The first ULA I read about was the one in the ZX81. The first ULAs that I saw were the pair in the BBC micro, mainly because we had Beebs at school but no ZX81.

Unlike PLAs, PALs, FPGAs etc the ULA is not field-programmable. It was, of course, 'programed' by the final metalisation layer. As such it was not suitable for prototypes or small production runs. The other devices were.

To tie in some of the other chips mentioned, the logic in the VAX11/730 processor is almost all PALs. There's also 8 2901 ALU chips (32 bit machine) microcode store RAM and an 8085 system to boot it. DEC fitted the logic onto 3 hex-height boards, say around 300 ICs.
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Old 3rd Aug 2021, 3:37 pm   #11
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Default Re: Early use of ULA's

I had dealings with AMD bit-slice 2901's in aircraft systems back in the late 70s and early 80s. They were used to implement 16-bit CPU's in the Tornado Autopilot computers and then in the Fly-by-Wire Jaguar Flight Control Computers, in both cases using a set of only 15 instructions.

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Old 3rd Aug 2021, 8:54 pm   #12
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Default Re: Early use of ULA's

I remember using a software package called QUDOS, Quick Design On Silicon, when at university, I believe that it was for Ferranti ULAs, this was in the late '80s so later than the ZX81. I seem to remember that to get a device manufactured was around £100 per device.

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Old 6th Aug 2021, 11:07 am   #13
NealCrook
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Default Re: Early use of ULA's

>>The later Master machines contain more custom chips which I think also came from VLSI Technology.

And VLSI technology ("VTI") went on to manufacture ARM CPU chips for Acorn/ARM, as one of the early "ARM Partners".
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Old 6th Aug 2021, 10:24 pm   #14
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Default Re: Early use of ULA's

I was involved with the manufacture of Ferranti ULAs, in 1973/4. We ran a pre-production line making small quantities for several well known firms. A couple I remember were Ford and Rolleiflex cameras. The Ford device was something to do with an automatic gearbox, perhaps an early form of ECU? The product for Sinclair must have been several years later, about 1981. I don't know if any of these early designs made it to mass production as I left the firm at the end of 1974.
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Old 6th Aug 2021, 10:38 pm   #15
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Default Re: Early use of ULA's

That is very interesting Bill and thanks all for the fascinating responses - so we just need to fill the Gap from 1974 to late 1980 when they must have started work on the 81 use of the ULA.
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