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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 6th Feb 2019, 11:41 pm   #1
julie_m
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Default BBC Master Programming Question

Just a quick question for anyone who was lucky enough to have got their hands on a real BBC Master 128 ..... (Or probably a Master Compact, which was basically a cut-down 128).

I'm currently doing a bit of a "retro programming" project. I can't say too much yet, but it involves a database. I'm hoping to shoehorn a version of it into a model B (without 6502 second processor), but it might well end up overflowing the 32K even if I use a cheaper graphics mode.

Am I right in thinking if you use one of the "shadow" screen modes on a BBC Master Series, you can just address memory linearly up to &7FFF (i.e., right through the space where the screen would be, in a "normal" graphics mode or on a Model B)? I'm sure that's the case, but I only ever had a Model B myself. And I'm after making this as compatible as possible ..... so I'm already using OS calls for input/output, not reading or writing the display directly, nor using any non-standard opcodes.
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Old 7th Feb 2019, 1:08 am   #2
mhennessy
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Default Re: BBC Master Programming Question

Yes, that's correct. Also true for the B+

I have a Master set up and working if there's anything you'd like me to check. Though I suspect that you can go a long way with the various emulators if you don't have access to the real thing. My favourite is this one - written entirely in JavaScript: https://bbc.godbolt.org/
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Old 7th Feb 2019, 2:07 am   #3
arjoll
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Default Re: BBC Master Programming Question

If you want a Master Compact let me know, I have the base unit (without power supply, drives etc) of one here that another local vintage collector didn't want - he specialises in Commodore.

I've now got a Master 128 (thanks to Paul Sherwin) so happy to send it over for the cost of shipping if you (or anyone else) has a use for it. Shipping would probably be about GBP60 though, and it would need the drive unit/power supply or know what to do to knock something up. No idea if it works.
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Old 7th Feb 2019, 11:27 am   #4
dominicbeesley
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Default Re: BBC Master Programming Question

That's right you can use all the memory from PAGE which is usually but not always &E00 on a Master through to &8000 when in a shadow mode

Mdfs.net has good documentation for memory layout see http://mdfs.net/Docs/Comp/BBC/AllMem

I can also recommend stardot.org.uk where there's a thriving ecosystem of developers and users

arjoll I'd love to have a compact but i suspect I'd be shot if i brought home another machine at this point. I'm sure somebody on stardot would give it a good home
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Old 7th Feb 2019, 4:09 pm   #5
julie_m
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Default Re: BBC Master Programming Question

Thanks for the confirmation. I thought that was how it worked, but didn't want to paint myself into a corner by assuming something that only later turned out to be wrong.

What I've written so far is working very nicely under emulation (BeebEm). I still seem to remember how to program 6502 assembly language pretty much off the top of my head, even! (The 6502 was the first processor where I tried riding the metal in earnest, having decided the Z-80 was too hard.)

Stardot looks like a very useful resource, thanks for that.
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