All,
I already own one broken DragonPlus where the PROM is dead - have just managed to obtain a 2nd - currently unknown condition but hoping the PROM is okay as if we can get a dump of a good PROM we have fix the 1st board.
If anybody else is in the UK and has access to a DragonPlus board then please let me know - desperate to ensure we can keep these working.
Regards
Simon
DragonPlus - Compusense
DragonPlus - Compusense
Simon Hardy
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Serenarian
- Posts: 29
- Joined: Thu Oct 25, 2012 1:28 pm
Re: DragonPlus - Compusense
As I mentioned in another post, I have one of these. KenH asked whether I have schematics for it. No such luck - but for those who haven't seen one I will attach some pics and a sketch of the board layout. Sorry I can't/don't want to remove the board and photo the top and botton track layout, but as you see they are neatly laid out and densely packed. No odd post production jumpers or cludges. Compusense did a good job. I don't think you would want to try to tackle building one but I've written out a shopping list for the ICs to give you a start!
I've had this board from new and fitted it to a custom Dragon 32 at first (upgraded to 64k and with added address decodes to match a Dragon 64). The Dragonplus board sits up on a long legged jumper socket that plugs into the Dragon's existing SAM socket. The SAM is in different positions on a D32 and D64 so the stand off jumper socket is either under PL2 (for D32) or PL3 (for D64) on the Dragon plus board. The SAM chip is relocated onto the Dragonplus board itself next to the 8 Dram chips. The ribbon cable that you see is plugged into one of the Dragon ROM sockets (IC34 on D64 or IC17 on D32) and the ROM itself is relocated to the Dragonplus board.
You will see that it uses a 6845 video chip - the same as the BBC and early IBM XT clones. I did some PEEKs at the registers in the past to compare with those two machines and found it quite easy to fathom out. For the character generation it uses an external ROM and someone has posted a dump of the basic character set. There is a second duplicate set with Underline and there is space for 2 additional character sets too. I did plan to make my own custom ROM with other characters - but never got round to it. The actual character layout is very simple to understand and a fairly standard 6845 implementation accessed through addreses FFE0 and FFE1.
The extra Dragonplus memory is bank switched into the lower 32k of the Dragon's 64k memory space as two alternate 32k banks. With the Dragons existing lower 32k memory that will give you three 32k banks from 0000 to 7FFF - and there is an additional 2k static video RAM bank used by the 6845. Bank switching is done through address FFE2. In practice you can either have two fast 32k RAM disks or (in theory) run 3 separate program spaces (provided that you copy and maintain the 0000 to 0C00 vectors into the alternate banks and reset the PC and stack pointer when you switch). Multitasking - well sort of?
I've had this board from new and fitted it to a custom Dragon 32 at first (upgraded to 64k and with added address decodes to match a Dragon 64). The Dragonplus board sits up on a long legged jumper socket that plugs into the Dragon's existing SAM socket. The SAM is in different positions on a D32 and D64 so the stand off jumper socket is either under PL2 (for D32) or PL3 (for D64) on the Dragon plus board. The SAM chip is relocated onto the Dragonplus board itself next to the 8 Dram chips. The ribbon cable that you see is plugged into one of the Dragon ROM sockets (IC34 on D64 or IC17 on D32) and the ROM itself is relocated to the Dragonplus board.
You will see that it uses a 6845 video chip - the same as the BBC and early IBM XT clones. I did some PEEKs at the registers in the past to compare with those two machines and found it quite easy to fathom out. For the character generation it uses an external ROM and someone has posted a dump of the basic character set. There is a second duplicate set with Underline and there is space for 2 additional character sets too. I did plan to make my own custom ROM with other characters - but never got round to it. The actual character layout is very simple to understand and a fairly standard 6845 implementation accessed through addreses FFE0 and FFE1.
The extra Dragonplus memory is bank switched into the lower 32k of the Dragon's 64k memory space as two alternate 32k banks. With the Dragons existing lower 32k memory that will give you three 32k banks from 0000 to 7FFF - and there is an additional 2k static video RAM bank used by the 6845. Bank switching is done through address FFE2. In practice you can either have two fast 32k RAM disks or (in theory) run 3 separate program spaces (provided that you copy and maintain the 0000 to 0C00 vectors into the alternate banks and reset the PC and stack pointer when you switch). Multitasking - well sort of?
- Attachments
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- Dragonplus board layout.JPG (424.63 KiB) Viewed 2998 times
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- Dragonplus image1.JPG (1.75 MiB) Viewed 3010 times
Re: DragonPlus - Compusense
Sorry for resurrecting this old topic, but thanks to Iksarfighter, we have now top quality scans of the Dragon Plus board, so I updated the wiki page.
Re: DragonPlus - Compusense
Hi guys!
I just dumped the character rom from Manu's board, and I was wondering if anyone can provide more dumps, as I'm not sure if the character rom is sort of universal or different countries had different roms.
You'll find attached a render of the character rom. Please report any differences.
Cheers,
Rob
I just dumped the character rom from Manu's board, and I was wondering if anyone can provide more dumps, as I'm not sure if the character rom is sort of universal or different countries had different roms.
You'll find attached a render of the character rom. Please report any differences.
Cheers,
Rob
- Attachments
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- DragonPlus_Chargen.gif (3.01 KiB) Viewed 2513 times