An Excess Of Questions

By Mark Bellis

Originally published in EUG #26

I have a few questions and comments:

Firstly on disks and drives, I am a little worried by the suggestion of a lack of support for broken 5.25" drives. Can you (or anyone at EUG) get hold of suitable 3.5" drives cheaply (preferably with PSU)? I would have to make a data duck device as my drive is a dual 5.25" type (or is one available?).

The question of disk formats is one which I have pondered at length. Given that only an Acorn machine has any hope of running a reasonable Beeb emulation of any sort, and that a 5.25" drive is available only for such units as an add-on for the A3000, now one of the older ARM machines, a 3.5" format seems attractive, especially with a view to leaping into the ARMs of a RISC PC (S'cuse the pun).

The RISC PC has only one 3.5" drive. Presumably because Acorn anticipated the migration from floppies to CD ROMs and other large storage media. (Another drive cannot be added as there is apparently no circuit board test point available for the drive selection line.) But perhaps a SCSI floppy drive can be added...?

Next it was mentioned that you bullied people whose programs will not run on a basic Electron. I must admit to being largely unaware of the facilities available on the unexpanded Elk - my only contact with one was playing Snapper on a friend's machine years ago. We had BBCs at school and I bought a Master 128 in 1988 so I am used to playing with Shadow RAM and pallette-switching etc...

With this in mind, could you publish a list of attributes of the unexpanded Electron as a guide for subscribers to program to? I'd like to know the following:

  1. What are the graphics capabilities of the Elk?
  2. Does it have all the Modes (0-7)?
  3. Is the screen mapped to &3000 - &8000?
  4. Is palette switching available (I know the Elk has no 6845 CRTC) via VDU19?
  5. What ports does the Elk have?
  6. If it has a User Port, what is its address?
  7. If it an analogue port, do ADVAL statements work as on the BBC? (I know the Master Compact has differences in port structure)
  8. What is the Elk's memory map like? Is it like the Master 128's?

I assume that readers' Elks:

  • have only the usual 6502 instruction set;
  • have no Shadow RAM or Sideways RAM unless a card has been added;
  • can run ROM cartridges the Master should be able to run too;
  • have an ADFS interface. What extra memory pages does it use (from &E00 upwards)?

Additionally, is the Elk's ADFS the same as the Master 128 ADFS? I realise the locations of disk controllers are probably different, so it would go no lower that OSWORD calls to the ADFS ROM if writing disk utilities.

I would like to know how many subscribers have which machines. This would give me an idea of how to pitch my contributions. (I assume that an Elk cannot run a 36-colour Mode 2 or a 16-colour 1 as a Master can with a little tweaking.)

Games. I saw someone had Citadel for sale. Is there a conversion for the Master 128? I have a version from my school days which I am trying to hack into to convert it, but no luck so far.

Does anyone know how the screen scrolling in Thrust works? I've tried some hardware scrolling in order to write a MICRO MACHINES-type game and the scrolling system in Thrust would be ideal. Unfortunately Thrust is EORed (as usual!) and it will be time-consuming to find the routine.

My programming doodles include a nearly complete version of COSMOGANG (an arcade game I played a lot at University) which is a Tetris clone with a difference. It uses screen poking for sprites and I'm not sure if it would work on an Elk. I will probably need to shift it to remove any Master-specific instructions too but, if it's worth it, I'll finish it off. It needs a joystick/keyboard routine to be integrated.

It runs in Mode 1 with standard colours at the moment and the gameplay is nice and speedy (in machine code).

Lastly, PCs and the like. Personally I prefer the Acorn machines - a RISC PC can emulate a 486 real time, or so they say. I don't want to make Bill Gates any richer either. By the way, what has happened to his "retiring on $2 billion and giving the rest to computer research"?!

However, having used VAX workstations (now and old system) at work, I rather fancy writing a GUI for my Master 128. Can anyone advise me about mice for my machine?

I assume that a mouse would use the User Port and run from a ROM or Sideways RAM image. Are there any serial mice for the Beeb? (I'd prefer that as I wish to use the User Port for robotics etc...)

With gratitude for all the hard work of typing in the bits you want to publish...

Mark Bellis, EUG #26

Thanks for your letter, Mark. 5.25" drives which will work on the 8 bit Acorn machines are not being made now and, while they can still be found, they will shortly be in short supply. I suggested that members would be advised to keep their 5.25" drives for when they really need them and try to get a 3.5" drive for general use. Brand new 3.5" drives can be had for £25 plus £2 P&P from Computer Junction, Arundel Street, Portsmouth.

Kits to fit these into 5.25" cases can be purchased from Maplin Electronics for £7.99 (Order code ZG47B) and should include a power lead to connect into a 5.25" power lead and a converter to connect to a 5.25" data lead. Mention EUG when you order, especially from Computer Junction.

One point: These drives, like most modern drives, are set up as DRIVE 1. To set a drive to DRIVE 0, remove the ribbon cable from the plug, unzip wires 10-16 and twist them around then re-assemble the plug.

The reason this works is that 10 = Motor enabled A, 12 = Drive B select, 14 = Drive A select, 16 = Motor enabled B. 11, 13 and 15 = Ground. Come to think of it, this should work with your A3000.

These drives use only a small amount of power but if you really need a separate power supply then you may find the circuit diagram in the Utilities section helpful.

Contributions to EUG should be done on your Word Processor and sent in on a disk. The CODE feature on each disk puts the text on the screen along with a number of other wonderful things. It comes courtesy of EUG's resident boffin Richard Dimond who, despite his modesty, is really smart.

I replace disks with a new branded disk. I need to keep the original submission disk. All the disks I use are of good quality from major disk manufacturers. I buy them in bulk, hundreds at a time and save some money.

EUG will publish anything members care to send, even political comment if that is what you want to talk about. EUG's editorial policy is very simple: submissions must not be copyrighted to anyone else and must not be deliberately offensive to anyone.

Your idea for a guide for new members is a good one. I will work on it.

The reason I ask people to ensure that programs run on the basic Elk is that the Elk is the lowest common denominator, so to speak, of the 8bit Acorns. It doesn't have Mode 7 and with ADFS, PAGE is at &1D00.

As you probably know, EUG members use a number of different machines. The Master comes with a full kit of extras while the Elk is a very basic machine to which you add extras as you need them. The Elk usually has ADFS but some readers have DFS. Almsot everything else can be added.

If you try to avoid Mode 7 and assume that the maximum amount of memory available will be that with PAGE at &1D00 then all the Acorn machines should have enough memory to run any programs you write. The Memory Map, all software commands, colours and graphics capabilities, assembly routines and everything else are more or less standard throughout the 8 bit Acorn range. The Elk however only has one sound channel.

Most long programs can be adapted to use less memory. Perhaps using disk overlays.

Having said all this, if you have something that will only run on the Master then please send it in anyway. There are a lot of readers using Masters, including me, who will appreciate it.

As for the various ports which some Elks might not have, don't worry about it. Programs which might use the User Port will be appreciated by those who have one. All Elks have the analogue port when the Plus 1 is attached (as it always will be to run the EUG disk).

Very interested in the games which you are developing. If you are not too sure if it will work on the Elk then send it in as a game for the Master and one of our many bright members will undoubtedly adapt it for the other machines.

As far as I know the mouse for the 8bit Acorn machines used the User Port and was of a type which is now difficult to find. Perhaps someone knows the exact type to ask for so that you can look for one. It worked with some software that was written into the program itself.

On the subject of the VAX workstation, was this the one made by Digital? If so, one of our members has one and would greatly appreciate any help or experience you have. Digital are very cagey about giving out any information.

Gus Donnachaidh, EUG #26