Compukit UK101 J1 Buffer Board

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tinplatepete
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Compukit UK101 J1 Buffer Board

Post by tinplatepete » Thu Nov 10, 2016 1:02 pm

Hi All.
This is a bait of a long shot but can anyone remember what ICs Premier Publications used on their J1 Buffer Board for a UK101, I am trying to recreate one of these cards from a picture but it’s a very poor image and doesn’t show the IC numbers, the board had four 16pin ICs on board that buffered all address and data lines also buffered the control lines i.e. IRQ, DD etc.
Any info would be useful
Pete
J1 Buffer Board.jpg
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flaxcottage
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Re: Compukit UK101 J1 Buffer Board

Post by flaxcottage » Thu Nov 10, 2016 3:52 pm

I've never seen one of these boards before. My Premier catalogue lists it as 'soon to be available'. However, looking at the board it appears that three of the ICs are grouped together. It is probable that these would be to buffer the address bus and will be hex buffers. The ICs would give 18 lines of which 16 would be needed.

The other IC, probably another hex buffer, would be for the clock, NMI, IRQ, R/W and possibly the DD signal. The data bus would not be buffered as it is already buffered by the 8T28s on the motherboard.

The buffers themselves are probably hex tristate buffers wired to act as simple pass through buffers. They will not be CMOS given the date. A suitable device could be a 74LS367.

Not much help, I know, but it should be quite easy to re-engineer such a board.
- John

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Re: Compukit UK101 J1 Buffer Board

Post by tinplatepete » Thu Nov 10, 2016 5:07 pm

Hi Many thanks for the reply.

On the OSI 610 board they have a similar circuit using 3 x 74365 & 1 X 7417, I could just replicate this circuit but I was trying to make the board as close to the premier buffer board as possible, the 7417 IC is a 14 pin chip but in the photograph all the ICs are 16 pin.

I agree that the data bus will be adequately buffed by the 8T28s but in all the adverts premier mention that the data bus is also buffered by this board, but this doesn’t make sense why they would do this.

I was going to just use 3x 74365s and work out what the other 16 pin IC would be, this will then buffer the address and control bus but then I read the advert about they also buffer the data bus, that’s why I thought I would ask around for advice or for any info before I start the build.

I can’t see any reason I can’t just use 4 X 74365s or 74367s to do the buffering.
Last edited by tinplatepete on Fri Nov 11, 2016 8:29 am, edited 1 time in total.
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Re: Compukit UK101 J1 Buffer Board

Post by flaxcottage » Thu Nov 10, 2016 8:14 pm

Sounds like you have a project! :lol:
- John

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Re: Compukit UK101 J1 Buffer Board

Post by tinplatepete » Fri Nov 11, 2016 8:25 am

Hi John.
Thanks for your input on what the ICs could be, your help is much appreciated, I’ll do some experimentation before I build the board, and hopefully someone may still have one of these boards or remember what ICs Premier used.
I lost my original UK101 about 10 years ago, I still have a few of the Premier EPROMS and a 32k Audio Computers Ram Card and some premier info but that’s about it, I am in the process of recreating that old machine from a poor quality photo.
Yes I do have a project.
Pete

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Re: Compukit UK101 J1 Buffer Board

Post by 1024MAK » Fri Nov 11, 2016 9:04 am

From a simply technical view point, there are a number of chips that could be used, as there are a number of line driver/buffer 74 series chips available. There were also line driver/buffer chips that were not part of the 74 series that would also do the job.

Data bus buffers should normally be located directly next to the MPU/CPU. Otherwise the address decoding has to be very specific (and often complex) to avoid more than one device attempting to drive the bus towards the MPU/CPU. So if the MPU/CPU board has data bus buffers, it's unlikely that any external boards would have had buffers on the data bus.

If the data bus did have buffers, the 74245 or 74LS245 is often used for this. But it's also possible to use other chips.

However, I can't help with which actual chips that Premier Publications used.

Mark
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Re: Compukit UK101 J1 Buffer Board

Post by flaxcottage » Fri Nov 11, 2016 10:16 am

There are some good photos of the UK101 here http://www.compukit.org/Motherboard_Versions which could be used to recreate the computer and then there is always this site http://searle.hostei.com/grant/uk101/uk101.html which has a condensed circuit diagram for the guts of a UK101. I used this to give my UK101 32K of CMOS static RAM and a 16K EPROM, combining BAS 1-4, BAS 5 and BAS-X.

If you are building from scratch then the inclusion of something like a 6522 could give you good I/O facilities.

Good luck.
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Re: Compukit UK101 J1 Buffer Board

Post by tinplatepete » Fri Nov 11, 2016 11:05 am

Sorry I should have mentioned in my last post that I have a replacement UK101 this the basis of the recreation, but I am still grateful for the info. Premier do mention that Buffer board should be located as close to UK101 as possible. 74ls245s do sound very familiar; I need to take a look at these.

I have uploaded a picture of the progress so far, in the picture you can see the 32k ram card, this card must have fallen of my old UK101 many years ago and survived in and old box as did the EPROMS, I replaced the capacitors on the ram card and it was ready to go, also you will see in the picture that my old EPROMS are mounted on a board under the UK101.
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UK101.jpg
Last edited by tinplatepete on Fri Apr 20, 2018 12:24 pm, edited 1 time in total.
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Re: Compukit UK101 J1 Buffer Board

Post by flaxcottage » Fri Nov 11, 2016 3:10 pm

Very nice and quite old school. My 32K card fits in the same place but is rather Heath-Robinson. :lol:
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32K upgrade UK101.pdf
(1.54 MiB) Downloaded 23 times
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Re: Compukit UK101 J1 Buffer Board

Post by tinplatepete » Fri Nov 11, 2016 4:38 pm

Hi John.
I’ve seen your card and I’m very impressed, if I couldn’t get my one working I was going to copy yours, I have a few more projects on the go for my UK101, I managed to borrow an Premier EPROM board to copy and I have the print layout for a Chromasonc Sound Card also I’m working on a 32 line switchable screen display as well as a CUA High Res Card.
The EPROM board I am using at the moment has 16k of EPROM space but is only temporary, that was always the good thing about a UK101 you build a temporary circuit but then it became permanent.
This will keep me busy for some time, Ill properly start a new thread with each of these projects at some point for anyone who is interested.
Pete

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Re: Compukit UK101 J1 Buffer Board

Post by jonb » Fri Nov 11, 2016 6:54 pm

Hi John

Your UK101 looks pristine, makes me wish I had one too. Oh, the nostalgic old school-ism of it! Lovely.

To assuage my angst at not having one myself (I wanted one way back in 1980, but my dad couldn't afford it so in the end I was given a ZX81 in kit form), I built a UK101 core using Grant's design and it is still working today (despite being wired point to point and nothing like as carefully as your expansion board!).

Hey ho. Not much point watching fleabay for one of these, because they always fetch more than I am willing to pay. An besides, I have never seen one as clean as yours.

Cheers
JonB

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Re: Compukit UK101 J1 Buffer Board

Post by flaxcottage » Fri Nov 11, 2016 7:39 pm

jonb wrote:Hi John

Your UK101 looks pristine, makes me wish I had one too. Oh, the nostalgic old school-ism of it! Lovely.
Yes I was very lucky. The UK101 was cased, which probably kept it clean. The previous owner(s) completed the RAM complement, upgraded the video display to 32 lines and added the 300/600 baud tape upgrade.

It cost a lot of money when I bought it but actually less than I was prepared to pay (though not by much!). It was a Christmas present from Mrs FlaxCottage a couple of years ago. =D>
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Re: Compukit UK101 J1 Buffer Board

Post by tinplatepete » Mon Apr 30, 2018 3:57 pm

In case anyone is interested I did manage to produce a prototype J1 Buffer Board based on the one by Premier Publications, it did work first time and I have started to make the final version, I used a fibreglass PCB to make it look as original as possible.
In the background of picture is the prototype of my J1 Mother Board, this is also based on the one made by Premier Publications.
The only info I had on these was a out of focus picture of my old machine and a Premier news letter and a vague memory of building these back in the day.
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Compukit UK101 J1 Buffer Board
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