"Outline specification for the BBC MICROCOMPUTER system"

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Richard Russell
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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Sun Oct 16, 2016 12:50 pm

RobC wrote:Several of us on here have working systems although they are quite temperamental!

How do you stop the helium leaking out, or have you managed to replace the laser with a semiconductor variety? I've heard stories of 'rejuvenating' HeNe lasers by leaving them in a helium-rich atmosphere for a while (so some helium leaks back in) but I've never been sure if they are genuine.

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby RobC » Sun Oct 16, 2016 1:33 pm

Richard Russell wrote:How do you stop the helium leaking out, or have you managed to replace the laser with a semiconductor variety? I've heard stories of 'rejuvenating' HeNe lasers by leaving them in a helium-rich atmosphere for a while (so some helium leaks back in) but I've never been sure if they are genuine.

It's still using the original laser as far as I know.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby jgharston » Sun Oct 16, 2016 1:38 pm

RobC wrote:The Domesday system uses mode 1 mainly and even has its own font for mode 2:
http://www.beebmaster.co.uk/Domesday/DFont2.html

Ooo, did it use those thin characters to get higher-colour modes? Eg:
Image

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

Richard Russell
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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Sun Oct 16, 2016 2:17 pm

RobC wrote:It's still using the original laser as far as I know.

I think you're jolly lucky that it's still working. I've found a reference to rejuvenating HeNe lasers in the American Journal of Physics (although only the abstract is available to read online) so it seems it's not a myth.

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby jms2 » Sun Oct 16, 2016 2:29 pm

jgharston wrote:Ooo, did it use those thin characters to get higher-colour modes?


Yes, it definitely did, but only under certain circumstances (when more colours needed, I suppose). This is something I remember seeing when I used one at school, and I remember being impressed by what I saw as "game author's" technique in a serious application. Also, the normal-width character set was subtly altered (eg, no slash through zeros).

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Sun Oct 16, 2016 2:41 pm

jms2 wrote:(eg, no slash through zeros).

Where's the Like button when you need it?!

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby RobC » Sun Oct 16, 2016 4:00 pm

Richard Russell wrote:I think you're jolly lucky that it's still working. I've found a reference to rejuvenating HeNe lasers in the American Journal of Physics (although only the abstract is available to read online) so it seems it's not a myth.

Just to be clear, I wasn't doubting you. Have to admit that this isn't something I was aware of but I'm happy to take your word for it.

I also have a Philips VLP-410 which is still working so I hope that between that and the Domesday player, I'll have enough parts to keep the system going for a while yet.

jms2 wrote:
jgharston wrote:Ooo, did it use those thin characters to get higher-colour modes?


Yes, it definitely did, but only under certain circumstances (when more colours needed, I suppose). This is something I remember seeing when I used one at school, and I remember being impressed by what I saw as "game author's" technique in a serious application. Also, the normal-width character set was subtly altered (eg, no slash through zeros).

The link I posted earlier shows the differences in the mode 1 fonts and says that the thin mode 2 font was used to display charts (where the extra colours are useful).

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Sun Oct 16, 2016 4:16 pm

RobC wrote:I wasn't doubting you.

I never thought you were; I did a Google search for my own interest. I know that Helium can leak through glass (slowly) and eventually this alters the mixture enough to stop the laser working. I expect keeping the machine switched off and in a cool environment helps to extend its life.

I wonder how the two machines at TNMOC are faring; they must lead a hard life and are probably more vulnerable to laser failure than yours.

Richard.

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IanS
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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby IanS » Sun Oct 16, 2016 4:30 pm

Richard Russell wrote:
RobC wrote:Several of us on here have working systems although they are quite temperamental!

How do you stop the helium leaking out, or have you managed to replace the laser with a semiconductor variety? I've heard stories of 'rejuvenating' HeNe lasers by leaving them in a helium-rich atmosphere for a while (so some helium leaks back in) but I've never been sure if they are genuine.


I always assumed the player used a solid-state laser, the switch-over from tube to solid-state was 1984 - https://en.wikipedia.org/wiki/Laserdisc ... technology

Are you sure the Domesday player was a tube?

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Sun Oct 16, 2016 4:44 pm

IanS wrote:Are you sure the Domesday player was a tube?

I can't say I'm 100% sure, no. I thought all Philips LaserVision players used HeNe lasers; if they switched to semiconductor lasers at some point I wasn't aware of it, although since CD players were around by 1986 the technology must have been available. Hopefully you're right, which might give them a longer life - until a mechanical failure anyway.

Edit: From your Wikipedia link: "In March 1984, Pioneer introduced the first consumer player with a solid-state laser, the LD-700" but I don't know about the Philips machines.

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Sun Oct 16, 2016 5:05 pm

Richard Russell wrote:I don't know about the Philips machines.

From what references I can find it looks as though the transition to semiconductor lasers was happening concurrently with the Domesday Project, which makes it hard to be sure one way or the other. I note that the HeNe lasers gave better video performance, which perhaps might have been a factor in this case. If anybody here with a working setup dares to take the top of the player I think it should be fairly obvious. If there's a gas laser it will be quite a large item, with a high-voltage feed, I would expect - and probably with a warning sticker.

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby danielj » Sun Oct 16, 2016 5:27 pm

Here you go:
http://www.beebmaster.co.uk/Domesday/DeadLVROM18.html

Doesn't look like there's a big old tube in there?

d.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Sun Oct 16, 2016 5:42 pm

danielj wrote:Doesn't look like there's a big old tube in there?

I would agree with you - if I were to guess on the basis of that photo I'd say it's most probably a semiconductor laser. If so, it worries me somewhat - given the nature of the video material - that (if Wikipedia is to be believed) picture quality may have suffered as a result.

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby RobC » Sun Oct 16, 2016 8:20 pm

Should have checked this earlier - in the circuit description section of the VLP415 service manual it says: "A Solid State laser emits a diverging laser beam"...

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Sun Oct 16, 2016 9:02 pm

RobC wrote:"A Solid State laser emits a diverging laser beam"...

Good to know for sure. I expect my recollection was of the Laservision players available at the start of the project, which would have been when they still used HeNe lasers. Sadly it doesn't eliminate laser aging as a cause of failure, and rejuvenation wouldn't be an option! But at least it shouldn't deteriorate whilst switched off. :wink:

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby algenon_iii » Mon Oct 17, 2016 12:22 pm

Richard Russell wrote:The information provided by schools included both photographs and text, and my recollection is that the textual content was displayed in MODE 7. But I can't be certain, and the only way of ascertaining for sure (in the absence of evidence from screen shots) would be to run up a working system - and I'm not sure there are any left (keeping the Helium-Neon lasers going was a real problem). It may be that the Camileon emulation would be another way of finding out, but I don't think that is available now either.



By coincidence Computerphile on YouTube put-up a video about the Domesday system at the weekend (the title is clickbait) and it looks like both the hardware and laserdiscs (the edges of one of discs shown appears to be 'rotting' away) are becoming a problem. They also show some other laserdiscs that were produced for the system that I was never aware of.
https://www.youtube.com/watch?v=VLh5LR0Kf1I

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby BigEd » Mon Oct 17, 2016 12:39 pm

There are screenshots from the CAMiLEON emulation and preservation effort here:
http://www.iconbar.com/articles/CAMiLEO ... ex937.html
and, linked from the video you offered, a video of the walk around Brecon, in the emulated environment:
https://www.youtube.com/watch?v=FV-GhqN7EFw

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Mon Oct 17, 2016 1:24 pm

algenon_iii wrote:By coincidence Computerphile on YouTube put-up a video about the Domesday system at the weekend

Interesting video but look at the comments! If I ever needed convincing that my refusal to give recorded interviews was justified....

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Commie_User » Mon Oct 17, 2016 3:20 pm

I saw that and found it very informative. I'm not clear what's supposed to be wrong with the comments but I thought the title was a superb example of clickbait. People use that word like it's a bad thing. (You want to get seen, don't you?)

It's whether the content's valuable that justifies a punchy title and it most certainly was this time. (But all the same, I'm holding one of my own potentials back - Two Beebs, One CUB - for asking if someone can make me a monitor switchbox! I'm not sure of my audience now!)

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby SteveBagley » Mon Oct 17, 2016 6:01 pm

Richard Russell wrote:
algenon_iii wrote:By coincidence Computerphile on YouTube put-up a video about the Domesday system at the weekend

Interesting video but look at the comments! If I ever needed convincing that my refusal to give recorded interviews was justified.....


I never (well, almost never) read the comments on the ones I do for Computerphile -- not worth the aggro :-)

Apparently, the TNMOC laserdisc player is temperamental and they wouldn't turn it on which is partly why the video is a bit dry as there's no real demonstration of it. If anyone has a working model near Nottingham please let me know…

Steve

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby BigEd » Tue Oct 25, 2016 2:36 pm

About Acorn's Basic developments, following on from this:
Richard Russell wrote:
hoglet wrote:Was Atom Super-BASIC not actually an early version of what became BBC Basic?
Or is it just another name for the Basic that shipped on ROM with every Acorn Atom?

I know no more than what can be deduced from that Acorn document, i.e. that Super BASIC was an "enlarged version of ATOM BASIC very similar in power to Microsoft, and with some extensions". So it definitely wasn't what was "shipped with every Atom", but you'd have to ask Sophie to what extent BBC BASIC was developed from it, or from scratch.

It's not even clear to me whether Super BASIC was ever an available product or just something that Sophie was working on at the time the BBC proposal was prepared. So it could be that it morphed into BBC BASIC before even being completed.


I found a quote from Chris Curry in an article in Your Computer (October 1981, lightly edited):
Before the BBC contract arrived Sophie at Acorn was writing a development of the Atom Basic which would have brought it more into line with languages such as Pascal and Comal. In the end, however, the BBC contract forced them to move back towards a Basic compatible with Microsoft.

“We have ended up with a compromise that doesn’t actually lose the features of Sophie's original ideas. We are confident that the Basic we are using for the BBC is as good as anyone can make it. It covers all of the Microsoft and all the good points of Sophie's original Basic. It meets just about everyone’s criteria of what they need out of Basic. It meets Microsoft 5; it does what Comal does; it is a structured Basic; it’s fast and it has upward-compatibility from the Atom Basic.


Nearby, from the June/July issue, there's an article by Martin Hayman "BBC's Proton Project and the Nuclear Family"
Controversy is still surging back and forth over the BBC's decision to put Acorn into the front-line by choosing an adaptation of its forthcoming Proton model as the "standard" micro for the 1982 series, Hands-on micros. Yet, as Your Computer has found, the programme makers are not daunted by the doubters and backbiters from the ranks of the microcomputer professionals and are pushing ahead with their initiative to popularise computing by putting it into every home.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby B3_B3_B3 » Wed Apr 19, 2017 1:57 pm

I always wondered about the bbc B's excessive amount of built-in ports (and thus unnecessary added cost for unused circuitry) e.g. many were unused on mine (disc and printer were eventually used):

Interesting that the beeb's outline spec seemed to specify a serial printer port rather than a parallel one, and analog port input rather than a digital IO port (i.e. bbc B user port) :

Oppositely, I would have chosen to specify a digital IO port (instead of analog) to allow users to plug in a (possibly optically isolated) ADC board etc so that mistakes vaporise a small cheapish board not part of the person's prized computer.
Also, surely learning how to control an ADC by wiggling its digital lines is also important.
An agreed(officially suggested) way of wiring Atari joysticks to user port pins could have allowed MOS/BASIC Joystick support.....
Also, I thought Centronics printers of the time were viewed as less hassle to setup than serial....
Also, without RS423 port perhaps serial UART IC could have been dropped from main board* and the cassette bit-banged like on Electron (but I suppose they were probably in a hurry_). *but moved to optional Econet daughterboard/section.

Would an extra internal '1Mhz' style Bus interface and IDC header for the Disc Interface have avoided needing disc interface specific ICs on main board, saving purchasing cost / giving smaller main board/ allowing design to be deferred/changed to 1770 later? Similarly for the econet section of board.
Also, it could be easier to attach a daughterboard to an IDC header than solder new chips to the motherboard.

Obviously the Tube(c) and 1Mhz bus were keepers. :)

Thats my observations/speculations for today.... :)

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby firthmj » Wed Apr 19, 2017 2:06 pm

Hi,

From the original document:

The BBC is investigating the possibility of
supporting a version of BASIC which is not implemented
yet on any single machine but which would be as
compatible as possible with existing practice and
could be made available within the public domain to
any manufacturer willing to implement it. The specification
in draft form is available on request. Meanwhile, you will
see that the most desirable 'fallback' is specified below.


Does anyone know whether the draft specification which was supposed to be "available on request" for BBC BASIC mentioned here exists anywhere anymore?
Had fun at the
Image
Meeting 13th May 2017

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Thu Apr 20, 2017 8:39 am

B3_B3_B3 wrote:could have allowed MOS/BASIC Joystick support.....

"MOS/BASIC joystick support" was provided from the beginning, using ADVAL (documented in the User Guide as being suitable for "games paddle" or "joy-stick" control). ADVAL(0) receives digital inputs (e.g. from 'fire buttons') and ADVAL(1) to ADVAL(3) analogue inputs (typically three joystick 'axes').

Also, without RS423 port perhaps serial UART IC could have been dropped from main board

The BBC would never have accepted that. The serial port was essential for 'professional' use and was one of the BBC's 'red lines' along with things like providing a broadcast-compatible baseband video output.

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby danielj » Thu Apr 20, 2017 9:01 am

B3_B3_B3 wrote:Would an extra internal '1Mhz' style Bus interface and IDC header for the Disc Interface have avoided needing disc interface specific ICs on main board, saving purchasing cost / giving smaller main board/ allowing design to be deferred/changed to 1770 later? Similarly for the econet section of board.
Also, it could be easier to attach a daughterboard to an IDC header than solder new chips to the motherboard.


This is the way the Atom had worked - you could use the machine in a basic state, or start plugging extra things in to gain more functionality, the pads already existing on the PCB. Econet was implemented as a plug in module by the time of the Master. Hindsight is, as ever, 20-20 with these things. At the time people make good and bad decisions about the way to do things in light of their current experience and/or requirements that are laid out before them. Lots of these observations seem to come from looking at the Beeb through the lens of the home-user, not the educational establishments etc that were actually the main consumers here.

d.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Coeus » Thu Apr 20, 2017 10:25 am

B3_B3_B3 wrote:I always wondered about the bbc B's excessive amount of built-in ports (and thus unnecessary added cost for unused circuitry) e.g. many were unused on mine (disc and printer were eventually used):


Most of the extra interfaces you say are typically unused are not present on the Model A, though this is only by omitting the components from the PCB - the space to fit them is still there.

If you wanted a machine with 32Kb of RAM without the extra I/O you could fit the extra RAM chips. Looking in the service manual dealers had instructions on how to create an A+ (my term) which had the extra RAM and the user VIA but none of the other options.

B3_B3_B3 wrote:Also, I thought Centronics printers of the time were viewed as less hassle to setup than serial....


For a personal printer, they were. I still remember going to a computer centre where we setting up equipment to capture screen dumps from a terminal - we attached a computer to the printer port and wasted much time because the technical guy at the centre concerned was adamant about the baud rate, strt & stop bits etc. Only when I fetched the protocol analyser and discovered what settings where really in use did we make any progress. You don't get that hassle with a centronics I/F. On the other hand the centronics I/F has limited cable length - you can't so easily sent to a printer in another room or even at the end of a modem.

B3_B3_B3 wrote:An agreed(officially suggested) way of wiring Atari joysticks to user port pins could have allowed MOS/BASIC Joystick support.....


I think this another question in the category of "Why was the BBC not better optimised for playing games" to which the answer is "that was not the focus of its design". For the TV series one would be much more likely to demonstrate controlling robotics via the joystick, hence the choice of an analogue one, capable of proportional control rather than Atari-style. It was nevertheless common practice to connect game-playing hoysticks to the analogue port and once you did that the OS support for a joystick would work fine.

B3_B3_B3 wrote:Also, without RS423 port perhaps serial UART IC could have been dropped from main board* and the cassette bit-banged like on Electron (but I suppose they were probably in a hurry_). *but moved to optional Econet daughterboard/section.


It may be a co-incidence but at the time I remember the BBC micro having much more reliable tape loading than some of the other machines of the time and it occurs to me this might be specifically because it uses a proper UART for the tape interface.

B3_B3_B3 wrote:Would an extra internal '1Mhz' style Bus interface and IDC header for the Disc Interface have avoided needing disc interface specific ICs on main board, saving purchasing cost / giving smaller main board/ allowing design to be deferred/changed to 1770 later? Similarly for the econet section of board.
Also, it could be easier to attach a daughterboard to an IDC header than solder new chips to the motherboard.


I think there is a clear design philosophy with the BBC micro to keep things neat by having things inside the single case and to me this is very much preferable to the mess of interconnected boxes that might otherwise have been. On the other hand, given that there was no room inside the case of 5 1/4" disc drives and therefore an external enclosure was needed, and given the later trend for having a power supply inside the case with the disk drives, it would have been a neater design to mount the floppy disc controller hardware on a PCB inside the enclosure with the drives and have that box then connect back to the BBC 1Mhz bus. It would also have been good to define an OSWORD interface for reading/writing raw sectors from the disk and formatting discs that wasn't tied to a specific FDC and didn't extend to doing trickery with the hardware, so that the choice of FDC would be up to whoever was supplying the DFS ROM to go with the disks. But hindsight is wonderful thing.

I am not sure the same would apply to econet - it's a simple cable connection so having the optional hardware fitted internally as required is preferable to external. On whether to put it on a daughter board I suspect the relative cost of PCB space vs. the semiconductors to go there was rather different than it is today.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby B3_B3_B3 » Thu Apr 20, 2017 12:33 pm

Coeus wrote:.....Most of the extra interfaces you say are typically unused are not present on the Model A, though this is only by omitting the components from the PCB - the space to fit them is still there.
.....
I think there is a clear design philosophy with the BBC micro to keep things neat by having things inside the single case and to me this is very much preferable to the mess of interconnected boxes that might otherwise have been.....

Sorry, I meant that each daughter board would neatly fit somewhere inside the BBC case (which would have a smaller main PCB use due to said daughterboards....). So still tidy.
And a smaller main PCB should be cheaper/more robust (less flexing)..... And expanding an A++ by fitting daughterboards would be easier than soldering in missing components.

For the DFS, perhaps like you say the DFS would have been better as an external '1Mhz Bus style' header: a completely external Disc interface might have encouraged even the official interface to be a PAGE at E00 one like the Opus....

Re Joysticks, I was thinking more of Acorn than BBC, but for experimenting I think a built in ADC is a mistake: you want experimenters to blow a cheapish replacable external board not damage the BBC main board, hence I would choose a digtal IO port over built in ADC


Richard Russell wrote:"MOS/BASIC joystick support" was provided from the beginning, using ADVAL (documented in the User Guide as being suitable for "games paddle" or "joy-stick" control). ADVAL(0) receives digital inputs (e.g. from 'fire buttons') and ADVAL(1) to ADVAL(3) analogue inputs (typically three joystick 'axes').....


Sorry, I was suggesting abandoning the built-in ADC for a (more replaceble) external one on a general purpose IO port as explained above: so was merely suggesting a way that joysticks could have been officially supported by Acorn.

Richard Russell wrote:The BBC would never have accepted that (no RS423). The serial port was essential for 'professional' use and was one of the BBC's 'red lines' along with things like providing a broadcast-compatible baseband video output.
I just meant that it was an option: I presumed affordability would have had some affect on the series popularity. Hence I wondered at the amount of built-in ports....

Finally, it seems quite unusual for the beeb to support one computer: it would almost have seem to have made more sense to specify a new subset of CP/M (ie with compatible graphics/screen) and same BBC BASIC that different manufacturers could then provide (z80 focus looks like the BBC may have originally thought that too?).....That would of course mean I might have learned z80 not 6502 assembly....to me the z80 always looks like a confused complicated non-orthagonal cpu (whereas the 6502 seems quite elegant for a deliberately cheapo CPU) : do you prefer writing 6502 or z80 BBC basics?
Last edited by B3_B3_B3 on Thu Apr 20, 2017 12:34 pm, edited 1 time in total.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby jgharston » Thu Apr 20, 2017 12:33 pm

Coeus wrote:It would also have been good to define an OSWORD interface for reading/writing raw sectors from the disk and formatting discs that wasn't tied to a specific FDC and didn't extend to doing trickery with the hardware, so that the choice of FDC would be up to whoever was supplying the DFS ROM to go with the disks.
It exists. OSWORD &7F. The DFS translates that to whatever hardware frobbing the hardware needs regardless of what that hardware is, the programmer just sees OSWORD &7F. As with the entire Acorn philosphy. Hardware specifics are hidden behind APIs, and as long as you behave yourself and use the APIs everything works.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby Richard Russell » Thu Apr 20, 2017 2:19 pm

B3_B3_B3 wrote:it would almost have seem to have made more sense to specify a new subset of CP/M (ie with compatible graphics/screen)...

The degree of compatibility required could only have been achieved using identical circuitry and identical firmware (we're not talking about a utopia where all application software operates through well defined APIs) so somebody would still have needed to design the guts of the machine before farming it out to different companies to apply their 'branding' (enclosure, keyboard etc.). I can't think of any commercial or economic model that could have achieved that, certainly not in the timescale.

z80 focus looks like the BBC may have originally thought that too?

The Newbrain, which everybody assumed would become the BBC Micro, was a Z80 machine.

to me the z80 always looks like a confused complicated non-orthagonal cpu

Non-orthogonal, yes (all 8080-derived CPUs have been, even to the present day with the 64-bit x86 architecture to a degree), but you say that as though it is a bad thing. My view is that with limited chip resources, and most software being hand-coded in assembler, being non-orthogonal had an advantage because you get a more flexible instruction set for a given gate count and op-code space (for example the auto-repeated instructions such as CPIR, LDIR etc. were only possible because of dedicating the BC register pair to 'count', the DE register pair to 'destination' and the HL register pair to 'source').

Richard.

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Re: "Outline specification for the BBC MICROCOMPUTER system"

Postby B3_B3_B3 » Thu Apr 20, 2017 6:44 pm

B3_B3_B3 wrote:it would almost have seem to have made more sense to specify a new subset of CP/M (ie with compatible graphics/screen)...

Replying, Richard Russell wrote:The degree of compatibility required could only have been achieved using identical circuitry and identical firmware (we're not talking about a utopia where all application software operates through well defined APIs) so somebody would still have needed to design the guts of the machine before farming it out to different companies to apply their 'branding' (enclosure, keyboard etc.). I can't think of any commercial or economic model that could have achieved that, certainly not in the timescale.

I had thought CP/M had a BIOS/API (I know it didn't really hide graphics differences), so perhaps same graphics hardware, perhaps same analog/user interface port hardware but I thought CP/M would allow a lot of commonality: so if manufacturer made a new graphic and interface port daughterboard/ main board they could have had a slice of BBC computer profit.... It seems perhaps CP/M was less impressive than I thought and so it was not worth the BBC commissioning an independent company to design a common BBC CP/M graphics standard and experimental interfaces (ADC /digital IO user port) circuit/board/standard? I had (mistakenly it seems) assumed that updating a CP/M computer's graphics circuitry and adding some common interface ports would be less work than building a BBC B from scratch whilst allowing any manufacturer who wanted a slice of the pie to have some. I suppose the CP/M manufacturers didn't think the pie was a big enough. I wonder if it was the computers in schools in the 80's subsidy that multiplied the pie size....

to me the z80 always looks like a confused complicated non-orthagonal cpu

Replying, Richard Russell wrote:[Non-orthogonal, yes (all 8080-derived CPUs have been, even to the present day with the 64-bit x86 architecture to a degree), but you say that as though it is a bad thing. My view is that with limited chip resources, and most software being hand-coded in assembler, being non-orthogonal had an advantage because you get a more flexible instruction set for a given gate count and op-code space (for example the auto-repeated instructions such as CPIR, LDIR etc. were only possible because of dedicating the BC register pair to 'count', the DE register pair to 'destination' and the HL register pair to 'source').

Hmmm, I had thought a machine compiler (perfect memory) would cope better a shortage of orthagonality than a human who must remember that one instruction can do something when another can't (even if desirable). Also, I read Mr Zaks z80 book (the opposite of the 6502 one I used to use) and he mentioned that the z80 loop instructions are slower and surprisingly not even more code efficient than a plain 6502 indexed loop: perhaps there are some counter examples he skipped...
The 6502 seems elegant to me, the z80 doesn't somehow: However I've never had to program a z80. I am guessing you prefer the z80 then :)


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