How good were Ferranti's ULAs at the time ?

Nagging hardware related question? Post here!
Brane2
Trump Card
Posts: 223
Joined: Fri Dec 30, 2011 5:42 pm
Location: Ljubljana, Slovenia

How good were Ferranti's ULAs at the time ?

Postby Brane2 » Mon Jul 19, 2021 11:25 pm

Could Sinclair have used them for much more than they did ?

I used to think Clive is a genius, but now looking from a distance, it looks like he could have done much better job with Spectrum and especially QL.

I've manage do dig out somewhere Ferranti's whitepaper on some model ( and lose it somewhere), but have no clue where did it lie in respect to what was available to Clive and what was to come next.

Does anyone have more data on that ?

For example, it looks like Z-80s refresh counter could have been used for video access with much less of a slowdown ( than in ZX-81, for example etc) and that with a teensy effort Spectrum could get much better sound and access to audio tape ( faster transfer speeds etc).

All while looking basically the same as it did then.
It could have had 128K option right from the start etc.

EDIT: I've found some documentation, talking about 15x15 cell arrangement ( each cell roughly with 1 flip-flop worth of things) and 40ish I/O cells.
Things came in 3 speeds one for 100-ish kHz operation, other for 3MHz designs and fastest one could go to 10MHz and had highest power consumption.
Which looks a lot like what Sinclair used.

But then there are docs, talking about 100MHz versions and up to 10kgate densities.
Has Sinclair ever seen those versions or were they just vaporware ?


On the journey of life I chose the psycho path...
Brane2
Trump Card
Posts: 223
Joined: Fri Dec 30, 2011 5:42 pm
Location: Ljubljana, Slovenia

Re: How good were Ferranti's ULAs at the time ?

Postby Brane2 » Wed Jul 21, 2021 7:59 pm

One more question - since ULAs of the time were pretty limited, both logic and pinwise, how feasible would be to package two dies in say PLCC68 or something like that ?

I have in mmind ensemble that would share power and some signal pins...


On the journey of life I chose the psycho path...
User avatar
tofro
Font of All Knowledge
Posts: 2172
Joined: Sun Feb 13, 2011 10:53 pm
Location: SW Germany

Re: How good were Ferranti's ULAs at the time ?

Postby tofro » Wed Jul 21, 2021 9:20 pm

PLCC was only standardized in 1984 (granted there were manufacturers already producing them), so you could expect them being rare and sockets and chips themselves more on the costly side - Nothing within Sinclair's interest range.


ʎɐqǝ ɯoɹɟ ǝq oʇ ƃuᴉoƃ ʇou sᴉ pɹɐoqʎǝʞ ʇxǝu ʎɯ 'ɹɐǝp ɥO
Brane2
Trump Card
Posts: 223
Joined: Fri Dec 30, 2011 5:42 pm
Location: Ljubljana, Slovenia

Re: How good were Ferranti's ULAs at the time ?

Postby Brane2 » Wed Jul 21, 2021 11:21 pm

tofro wrote:PLCC was only standardized in 1984 (granted there were manufacturers already producing them), so you could expect them being rare and sockets and chips themselves more on the costly side - Nothing within Sinclair's interest range.


Atari had couple them ST ( MMU, GLUE).

Not that Sicnclair cared much about standards. He would happily use any plastic blob, provided it's functional.


On the journey of life I chose the psycho path...
Derek_Stewart
Font of All Knowledge
Posts: 2354
Joined: Mon Dec 20, 2010 11:40 am
Location: Runcorn, Cheshire, UK

Re: How good were Ferranti's ULAs at the time ?

Postby Derek_Stewart » Thu Jul 22, 2021 9:03 am

HI,

Which ULA are you talking about?

8301 or 8302

I did think about doing this a while ago. But I due to the conversations, I thought it was being done by others.

I will put this on the list of jobs...


Regards,

Derek
Brane2
Trump Card
Posts: 223
Joined: Fri Dec 30, 2011 5:42 pm
Location: Ljubljana, Slovenia

Re: How good were Ferranti's ULAs at the time ?

Postby Brane2 » Thu Jul 22, 2021 11:20 am

Derek_Stewart wrote:HI,

Which ULA are you talking about?

8301 or 8302


About the Ferranti's die that Sinclair has used for them.
What was it capable of ?

Which models were accessible to Sinclair at the time ?
All I can find on the net is one model, with 40-ish I/O cells and 225 ( 15 x 15) internal, "logic" cells, each consisting with IIRC 3 transistors, couple of diodes and resistors.


On the journey of life I chose the psycho path...
Brane2
Trump Card
Posts: 223
Joined: Fri Dec 30, 2011 5:42 pm
Location: Ljubljana, Slovenia

Re: How good were Ferranti's ULAs at the time ?

Postby Brane2 » Thu Jul 22, 2021 11:23 am

Going more extreme route, could Sinclair have done prehistoric APU version, joining four ULAs in the package and realizing some simple form of 16/32-bit CPU, memory controller and video shifter in one package ?


On the journey of life I chose the psycho path...
Brane2
Trump Card
Posts: 223
Joined: Fri Dec 30, 2011 5:42 pm
Location: Ljubljana, Slovenia

Re: How good were Ferranti's ULAs at the time ?

Postby Brane2 » Fri Jul 23, 2021 3:51 pm

Anyone with an idea about how many metallization layers were allowed ?
Just one or more ?
Ferranti seems to imply that one layer is all that it is needed, but it's obvious that this can't cover every use case.

It's also very suboptimal.
So, waht happens when more than one layer is needed ?
Were up to N layers included into price, was there a maximum or is maximum 1 layer ?

BTW, it would be fun to make ULA PCB with discrete SMD BJT, schottkys and resistors to simply check what could be done with it...

IS there any data on reistor values, transistor characteristics etc ?


On the journey of life I chose the psycho path...
Nasta
Gold Card
Posts: 354
Joined: Sun Feb 12, 2012 2:02 am
Location: Zapresic, Croatia

Re: How good were Ferranti's ULAs at the time ?

Postby Nasta » Tue Jul 27, 2021 12:38 pm

Ferranti (later Plessey) ULAs were un-committed transistor+resistor logic loosely based on ISL logic specs. It's not exactly TTL but similar, has some current steering tricks like ECL. There are a number of die photos available on the net. It would be very difficult to re-create exactly with discrete transistors because it used multi-emitter transistors with emitter size and geometry designed for particular current distribution.
This is quite different than what was used later by LSI logic and even later Toshiba, where the design is a 'sea of gates' one, having already constructed basic gates in NMOS or CMOS which are then connected by metal layer(s).
From what can be seen on the dies, Ferranti clearly used only the final layer to connect the parts. There are a number of buried features in the silicon that can be used as jumpers (multiple connection openings in the SiO2 layer for some parts). There also a metal layer under the SiO2 that provides power, and it seems some sort of bus structure to IO cells (this is similar to what would be later used in FPGAs).
One 'advantage' that these ULAs had was that you could, to an extent, do some analog functions in them if that saved gates.
Apparently there is a book available (behind a paywall) that explains how circuits are designed to fit a ULA.

Now, during the years I have been exposed to some info on how the circuits were designed, but given the 'leaky dynamic RAM' nature of the human brain, take this with a grain of salt:

Ferranti/Plessey only had >40 pins cases in it's later stages of the ULA story (before they got out of that business), in particular 48 pins and 68pins, but these were initially offered only as LCC, which is a very expensive 'upside down' version of what would later become PLCC68, and that was indeed used in the Acorn Electron, and it was one of the reasons for many problems. You can find pictures of the Electron PCB with the very expensive LCC socket for the even more expensive LCC ULA which tended to run very hot (as bipolar logic of that kind does). Even at that pin count the ULA was pin count limited so the Electron actually uses 4 bit wide DRAM (64k x 4) to implement it's 32k of RAM, which was one more reason for problems.

I seem to remember one f the creators of the Spectrum talking abut ULA development, and the problem with that is that they were not exactly developed by Sinclair but rather by Ferranti, most of the circuits would be bread-boarded in TTL by people at Sinclair (albeit with foreknowledge of the future integration int an ULA) and then People at Ferranti would take over. Apparently there was some sort of rudimentary CAD involved running on a mainframe to assist with routing and possibly some simple simulations? I do remember that this was a relatively big point of contention which also forced Sinclair's hand when choosing who would be doing the custom chips, I am guessing that there must have been some sort of financial agreement regarding man and machine hours bought by Sinclair from Plessey, as by the time the QL was made, there were some other options. Sinclair being Sinclair, they almost certainly opted for what cost less at the time, and that would be Ferranti because of existing knowhow. Once Amstrad came along, LSI was already working as well as standard cell custom chip manufacturers that could translate a TTL design to single chip silicon almost literally (If I remember right, Chips and Technologies was one of the first in that field, from this point in time it is hard to believe they would eventually, by a very circuitous route become the giant that today is TSMC).

Could the resources of the given Ferranti ULAs have been put to better use and more features could be crammed into the 8301 and 8302? I am certain that some fairly small but important things could have been implemented that never the less could have brought substantial improvements in performance, if there was more time - but I doubt it would be anything major and drastic. I suspect that most of the ULA development would have been efficient routing, and this is always the major problem as getting sufficient man or machine power to do this was very expensive at the time. While there were revisions of the 8301, I guess once the motherboards were committed, little could be done to add significant functionality while keeping compatibility. Though, I am quite certain the RAM timing could have been improved and some speed added, even with existing RAM.

Also, as I have speculated before, there is some evidence that the 8301 and 8302 were initially intended to be a single chip, one of the biggest clues is the way PCEN is derived as well as the initial QL motherboards connecting the 8302 data bus to the RAM data bus, which is exactly how it would have been internally connected in the same chip. It is highly likely that Sinclair abandoned the idea having seen what Acorn got themselves into with the Electron.

Finally, there is the question of re-creating the ULAs with modern chips. This is certainly possible for the 8301, there is more than sufficient data to not only re-create it but also improve on it. Using a 3.3V FPGA to do this is not a huge problem with the 8301 as there is a limited number of signals that need converting form 5V to 3.3V TTL and all the lines except the RGB and HV synch can be driven by 3.3V outputs from the FPGA. In most places resistive divides and Schottky diodes would do the trick, which was also used on the ZX81 and Spectrum ULA replacements offered on the retro market. The 8302 is a bit more tricky as some deep diving into system software and some collection of data from multiple sources to get the IPC and microdrive circuitry right. The 8302 actually has one superfluous pin - it has both PCENL and DSMCL and actually only needs one to decode properly given a correct implementation of PCENL in the 8301. Alas, I think that both are needed for compatibility on a QL motherboard since one cannot guarantee which motherboard and 8301 version will be used.



Who is online

Users browsing this forum: No registered users and 4 guests