BeebSID

discuss both original and modern hardware for the bbc micro/electron
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MartinB
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Re: BeebSID

Post by MartinB » Fri Nov 13, 2009 7:34 pm

Cheers Alan - I've had a read of the datasheets and understand now so I'm happy to go with your latest suggestion :D

So, I've updated the schematic with the new MOSFET part number and that doesn't cause any wiring change. However...

...all those who have been checking this over for me are fired. In fact sod it, I'm fired too :lol:. I wanted to freeze the schematic at Issue 1 Final so I went back to the prototype and did a full pin-for-pin comparison and noticed some err..., errors :oops:. Trouble is, it's all too easy with electronic drawings to do things such as rotating connectors and at some point I obviously did this to the 1MHz bus connector for clarity but didn't flip the corresponding SID pins. Hence, the address and data pins (A0-A4 & D0-D7) were reversed! I also noticed that some idiot labelled the Nor gates as a 74LS32 when it's actually a 74LS02 #-o and I've added an absent ground connection to Pin 1 of the bus connector which is especially desirable if the BeebSID is not being powered from the Beeb.

Anyway, I have now checked and re-checked and am happy that the attached Issue 1 is the final schematic. For completeness, I have labelled the required 1MHz bus signals since I realised that I could move the labels away from the pin numbers so it's not cluttered as I suggested. (Full parts list to follow.)
BeebSID Iss1_s.JPG
BeebSID Iss1_s.JPG (29.67 KiB) Viewed 3508 times
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sirmorris
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Re: BeebSID

Post by sirmorris » Fri Nov 13, 2009 7:55 pm

Fabulous stuff!

See you on Sunday at RCM?

C

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MartinB
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Re: BeebSID

Post by MartinB » Fri Nov 13, 2009 9:14 pm

Why thank-you sirmorris :D

Actually, as I'm sure you can see, it's only a fairly simple circuit and to people in the know it probably seems as if I'm making something of a meal of it :roll:. Thing is, I'm (a) trying to learn the whole fag-packet to PCB process and (b) do it all 'in public' for the benefit of novices. I think I sketched the original design in about an hour and built the prototype in less and normally that would be it for me so this 'professional' approach sits uncomfortably with me.

Oh well, we'll get there in the end and hopefully we can then form a community SID orchestra - I'm sure Tom will mix something suitable :wink:

Sadly, I can't make RCM but I look forward to hearing all about it....

Martin

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Re: BeebSID

Post by AlanD » Fri Nov 13, 2009 11:21 pm

hello martin

pity you cant make RCM

sadly i will have to ask every one thier names again

AlanD

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MartinB
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Re: BeebSID

Post by MartinB » Sun Nov 22, 2009 11:05 pm

Yes, things are progressing in the background :D

I thought Sudoku was tough but this manual routing puzzle has been doing my head in...
bs.JPG
bs.JPG (49.53 KiB) Viewed 3327 times
Entirely manually routed and it all checks out against the schematic - fortunately the testing is a complex automated process courtesy of DipTrace :D

It's not quite finished yet, the phono socket at the top left needs to be a DC barrel connector, I need to confirm the pad spacing of some of the analogue discretes and it's missing a spot of ground plane and the text stuff. Other than that, coming on a treat I think :D

Since this is my first attempt at anything even slightly complex, does anything untoward jump out at the experts...?

Martin

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Re: BeebSID

Post by retroclinic » Sun Nov 22, 2009 11:18 pm

=D>


:-k


Termination resistors? You probably didn't use any on the prototype, but I think with 1MHz bus stuff, they're always a good idea to add - even if you add just the pads, and especially since you're doing a hard wired pass-thru.

I made that mistake with the original IDE PCBs, I didn't put any terminators on the board, as I prototyped it with some Lattice GALs, and all seemed well. When I came to build them, all was well with Lattice GALs and TI PALs, but I found a few tubes of AMD PALs, and used those..... [-X ...they went berzerk. Seemed the overshoots were causing problems internally, and I had to manually add a set of pull down's on the input pins as I built those boards. You may find that one manufacturer of TTL will work no problem, then someone uses a different one, and will have trouble. It also depends on the cable length too - the longer the cable, the more the overshoot will be.

Just a thought....nice work on the PCB tho! Mark.
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Re: BeebSID

Post by MartinB » Sun Nov 22, 2009 11:30 pm

Hmmm... that's depressing :( but I do remember you mentioning it.

Do you think they're necessary on all signals or just certain ones? I think I'll be struggling a bit for routing space on two layers unless they're a bit scattered. Are you suggesting they might be needed if the pass-thru isn't connected to a subsequent device and in which case, could we not (collectively) propose a floating terminator plug with resistors in an IDC plug for use on the last device if you get my drift :-k

( Are we talking signal-to-ground for everything btw? )

Martin

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Re: BeebSID

Post by retroclinic » Mon Nov 23, 2009 6:10 am

Hi.

My personal suggestion is to lose the hard wired pass thru, and put terminators in there instead. They're needed for the address and data lines - not for the others. The termination, according to Acorn Spec, should be one set of pull-ups, and one set of pull downs, so you use 4 resistor packs in total. Values of 2k2 to 4k7 should be fine.

Take a look at the DC board you've got, you can see the 4 resistor packs next to the 1MHz connector. When I make the external boxes, those resistor packs are in sockets, so they can be removed if a pass thru is required. I just use an IDC header attached to the ribbon cable if a pass thru is requested, that saves on board space for the 90% of users who are never going to need one.

Mark.
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MartinB
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Re: BeebSID

Post by MartinB » Mon Nov 23, 2009 11:03 am

Ok Mark (et al), I've done some research into the termination issue and my findings and thoughts are as follows...

A quick straw poll of devices reveals that the Acorn TTX adaptor has terminations but no pass-thru. (According to the 1MHz App. note, this device is designed to be last in any chain and hence has hard-wired termination.) An Opus Challenger has no terminations (or provision) but has pass-thru and the DCP Interpacks have no termination (or provision) and have proprietary pass-thru. Therefore, partly because I do want pass-thru but don't want to make the board any bigger or more complicated, I'm not going to include provision for terminations. What I will do though is, as I suggested, detail how to make an IDC plug-in terminator for use on any 1MHz devices which have a second connector and are last in the chain.

I use the Challenger a lot and did test the SID prototype connected through the Challenger without any problems so all things considered I don't think the amount of effort required to terminate BeebSID justifies the very marginal conditions where termination might be required. When I scoped all the signals, there was no increased ringing or overshoot on the bus and the only thing I wasn't happy about was the long-sufering R/W and 1MHzE which are now buffered with the LS04.

So, I'm now sitting firmly in the Opus and DCP camps and am going with the (unterminated) flow :wink:

Martin

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Re: BeebSID

Post by MurrayCakaMuzer » Wed Nov 25, 2009 6:27 pm

Sorry, I'm a little confused - when are terminators needed? When the BeebSID is the last in the chain of more than one is my guess, is that correct?

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Re: BeebSID

Post by MartinB » Wed Nov 25, 2009 7:13 pm

I'll almost guarantee that they won't be needed but at least in theory yes, the farthest point of a bus normally has termination applied to prevent possible erratic behaviour of the individual lines of that bus. A single line termination is two equal value resistors connected in series from Vcc to ground with a bus line connected to the centre junction - i.e. that line is 'held' at a potential of Vcc/2. The resistor values are relatively high such that the bus drivers can still pull the line high or low as required but effects such as noise, cross-talk, overshoot, ringing and reflections will be minimised.

Mark was quite right to point out that Acorn's specification for 1MHz bus devices advises termination of the last device. Personally, I have never found any problems with my own projects or with the example devices I mentioned such as the Challenger or the DCP interfaces. However, to cover all bases, I am suggesting that we can make a terminator using a 34-way IDC socket populated with these terminating resistors and this plug can then be used (or not) as required.

Martin

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Re: BeebSID

Post by retroclinic » Wed Nov 25, 2009 7:15 pm

MurrayCakaMuzer wrote:Sorry, I'm a little confused - when are terminators needed? When the BeebSID is the last in the chain of more than one is my guess, is that correct?
Hi. Pretty much, yes.

The 1MHz bus can be used by various devices, and like floppy drives, or even SCSI, it "should" be terminated at the last device, to prevent reflections and overshoots from passing back down the line. However, when there's only 1 device and a shortish cable, you can usually get away without using them.

Mark.
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Re: BeebSID

Post by MartinB » Wed Nov 25, 2009 7:23 pm

Actually, SCSI was one area I was looking at - we use lots of daisy-chained configurations at work and the individual devices tend to either have a switchable termination or, more commonly for the boxes we use, there is a plug-in termination much as I'm suggesting for fitment to the pass-thru connector of the last device. I think that would be a more flexible solution than juggling resistor packs or being forced to use devices in a certain order?

Martin

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Re: BeebSID

Post by retroclinic » Wed Nov 25, 2009 7:31 pm

The thing with plug in terminators, is someone has to sit down and make them. If you provide pads on the board for resistors, you don't need to fit them if you don't want to, but the option is there, and it doesn't cost anything apart from a small bit of board space. You can then - if needed, make one or more with sockets and resistors - and it's much easier than making a terminator up from a 34 way IDC socket.

Of course it's up to you, but if it was me, I would have lost the extra 34 way connector and put pads for resistors there - as I've done in DC - and if a pass thru is needed, then a 34 way header is used on the cable.

Mark.
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Re: BeebSID

Post by MartinB » Wed Nov 25, 2009 8:15 pm

Hmmm.... :-k

You've soldered terminations onto DC so it can't be used with another terminated device unless one desolders the packs or, DC has to be the last device in a chain of unterminated devices. If we solder terminations onto BeebSID then we have the same problem and I agree that there would then be no point in having a pass-thru. However, I would expect to have BeebSID as a permanent peripheral (and hope many other people will) leaving it's pass-thru for use with other devices and given this, BeebSID would either have to have socketed resistor packs or use a plug-in terminator.

As an aside, I think that Acorn copped out (for cost saving) with the TTX adaptor in that they soldered in their terminations and dropped the pass-thru claiming that they 'designed' it to be the last device :^o

I can see pros and cons for both arguments here but on balance, I feel that leaving BeebSID unterminated with pass-thru is my preference. It's no hassle for me to change the board, dropping the pass-thru and adding termination pads but I can't have both on a (small) two-layer board.

Ok people, this is a non-profit non-commercial activity, boards will cost [ Value of Martin's cheque / Number made ]. If you are technical and/or can follow this discussion and/or want a board when they're ready, please stick your oar in now please... :wink:

Martin

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Re: BeebSID

Post by retroclinic » Wed Nov 25, 2009 9:03 pm

Hi.

Yes, on the internal and pre-fitted kits the terms are soldered in. On the External units the terms are in sockets (apart from the 2 prototypes), so I (or the user) can add a pass thru at a later date (or at build time).

And put me down for a board please :D

Thx, Mark.
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Re: BeebSID

Post by MurrayCakaMuzer » Wed Nov 25, 2009 9:34 pm

Sounds like it's all sorted then!

Any idea how long it might take to get them on sale?

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Re: BeebSID

Post by MartinB » Wed Nov 25, 2009 10:24 pm

Murray wrote:Sounds like it's all sorted then!
It is..?
...and wrote:Any idea how long it might take to get them on sale?
Well first of all, is that a "Yes, I want one." ? :D
Mark wrote:And put me down for a board please :D
Of course, you were going to get one whether you wanted one or not :wink:. Mind you, if it's just us two then they're going to be F*%!$#g expensive :lol:

Martin

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Re: BeebSID

Post by MurrayCakaMuzer » Wed Nov 25, 2009 10:56 pm

MartinB wrote:
Murray wrote:Sounds like it's all sorted then!
It is..?
Well, as far as the actual design is concerned (other than the terminators)
...and wrote:
...and wrote:Any idea how long it might take to get them on sale?
Well first of all, is that a "Yes, I want one." ? :D
Yep ;)
...and wrote:
Mark wrote:And put me down for a board please :D
Of course, you were going to get one whether you wanted one or not :wink:. Mind you, if it's just us two then they're going to be F*%!$#g expensive :lol:

Martin

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Re: BeebSID

Post by Elk Towers » Thu Nov 26, 2009 7:17 am

I would like one to add to elk towers 8) please and depending on cost I would prefer a ready built one, or at least one with el SID already fitted



Nick
Nick

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sirmorris
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Re: BeebSID

Post by sirmorris » Thu Nov 26, 2009 8:20 am

Bare boards for the lads? That's a big YES from me please!

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Re: BeebSID

Post by AndyRCM » Thu Nov 26, 2009 8:40 am

I would be interested in one - to show off at RCM! :)
Depending on price of course ;)

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Re: BeebSID

Post by andyt31 » Thu Nov 26, 2009 9:23 am

Im interested too. Happy to build my own and I have a spare SID chip! :)
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MartinB
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Re: BeebSID

Post by MartinB » Thu Nov 26, 2009 11:29 am

Thanks for the positive responses thus far :D and here’s the plan I had in mind for BeebSID

Since it’s a peripheral based on fun rather than functionality, I see it as something that would hopefully become pretty much a ‘standard fit’ in the Beeb community. This would then for example encourage authors of new RS games projects to include support for the SID which would significantly enhance their appeal. Anyway, you get the idea… :)

Now, I didn’t want to embark on this as a closed-door commercial project and emerge at the other end with yet another appealing-but-expensive gadget which is one of my reasons for working this ‘in public’. As soon as the PCB layout is finished, I’ll get some quotes and will be able to provide a near-as-dammit (no-profit) cost for a single bare board. For that cost to be viable, I will need to be ordering a reasonable quantity and hence will need to know in advance that a good proportion of them will be taken by folks on here. I don’t mind standing a few unclaimed boards on the assumption that sooner or later they’ll be taken but I’m not going to stump up for dozens and get stuck with them.

Of course, a big issue here is that not everyone who wants a BeebSID has the skills to build one even from a PCB. Therefore, I would like to propose/ask/appeal/hope that those of us who can build one will offer to do one or two more for the needy. There’ll perhaps need to be some sort of co-ordinated effort with regard to ordering components so that we don’t end up paying many times over for p&p on small orders but that idea’s open to suggestions?
Nick wrote:...and depending on cost I would prefer a ready built one, or at least one with el SID already fitted
I'm hoping that the cost of a built unit will be pretty much the cost of the PCB plus parts but that'll be up to the individual builders. SID chips are of course a significant issue and I should say now that I don't have any to offer around. If anybody has any spare then hopefully they will make them available at a fair price once we're up and running?
Charlie wrote:Bare boards for the lads?
Yep, exactly that :D
Andy (RCM) wrote:Depending on price of course :wink:
Accepted as a potential project killer :( - that's why this is definitely a case of 'the more the merrier' [-o<
Andy (t) wrote: Happy to build my own...
And maybe another...? :wink:

I've nearly finished the PCB design (just juggling things to see if I can squeeze these wretched termination packs on there :wink:) and then I'll do a final post for scrutiny and comment before embarking on getting quotes. Not too far away now then... :D

Martin

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Re: BeebSID

Post by andyt31 » Thu Nov 26, 2009 11:35 am

Im sure I can build one or 2 more for the 'needy' :D As long as P&P is covered and a couple of quid for my time.

@AndyRCM - we should ask Phu who he used to get those VIC-20 boards made up. Sounds like he got a good price for the PCB build.
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Re: BeebSID

Post by sirmorris » Thu Nov 26, 2009 11:53 am

I'll be happy to perform build duty.

I'll take 2 boards now I think about it. Saying that, how would you/the community feel if people like me went on to sell a board or 2 on the open market?

C

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Re: BeebSID

Post by iomanoid » Thu Nov 26, 2009 12:07 pm

Whoah! I've been a bit preoccupied with "life" lately... turn my back for a little bit... and now it's all almost done!! Splendid :D

Needless to say, I'm definitely up for one, maybe 2, maybe even more later. One hundred percent one to start off with though, and I'm another one who would really appreciate someone doing the fiddly wizard bits, as I can't solder for shit nor shovel. I've got my own SIDs.

Is it OK to start getting excited yet?

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Re: BeebSID

Post by MartinB » Thu Nov 26, 2009 2:58 pm

iomanoid wrote:Is it OK to start getting excited yet?
Yes, but let's be grown up about this and keep it low key for now....ImageImageImage

Charlie wrote:...how would you/the community feel if people like me went on to sell a board or 2 on the open market?
For profit ? :shock:. You've just defiled the organic innocence of Tom Walker's BeebSID even whilst it's still in the womb - may shame be upon you [-X ( Let's all discuss that much further down the line eh? 8) )

Martin

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Re: BeebSID

Post by sirmorris » Thu Nov 26, 2009 4:18 pm

For profit ? :shock:.
You'd better slap a creative commons licensing agreement on this all then; otherwise someone'll be doing a turbo version some time soon :wink:

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Re: BeebSID

Post by MurrayCakaMuzer » Thu Nov 26, 2009 5:09 pm

CC-BY-NC-SA would be the one to use, does the below sound good to you MartinB?

http://creativecommons.org/licenses/by-nc-sa/3.0/

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