MAME - Dragon Plus

[Pernod70]

I'm emulating the Dragon Plus board in MAME and have a few questions. Hopefully someone with experience with this board can help.

I've attached a couple of current screenshots running FLEX from the archive to show what it looks like at the moment. With the board installed there are effectively two video outputs, the original VDP and the 6845 on the board. MAME shows both outputs side-by-side as you need the VDP screen to initially load anything.

0001.jpg (125.11 KiB) Viewed 8566 times

0003.jpg (155.4 KiB) Viewed 8566 times

And now the questions ...
- the board has a PROM, what is this used for?
- my VDP output gets garbled whilst running FLEX, is this expected?
- can anyone suggest a test to find out whether my bank switching is correct, and actually finds the extra 64K?

[Pernod70]

Some more progress:

FLEX.jpg (26.39 KiB) Viewed 8546 times

EDIT128.jpg (37.06 KiB) Viewed 8546 times

It looks like I've fixed my banking issues and the VDP output no longer gets corrupted.

Outstanding questions:
- the board has a PROM, what is this used for?
- what does the cursor look like, a solid block or an underscore as in my EDIT+ screenshot?
- can anyone suggest a test to determine whether the extra 64K is being found?

[robcfg]

Hi!

Cool progress on the Dragon Plus emulation!

I haven't been able to test the board on my Dragon 64, but I'll try to get some more info for you next week.

Cheers,
Rob

[Pernod70]

I haven't been able to test the board on my Dragon 64, but I'll try to get some more info for you next week.

Thanks.

I also tried the OS9 for the Dragon Plus from the archive. It doesn't even switch to the plus videoram to write anything to it. Not sure whether this is due to GO51 not being found or maybe a bad floppy image.

OS9.jpg (39.1 KiB) Viewed 8536 times

[robcfg]

- the board has a PROM, what is this used for?

No idea, but must be related to ram mapping. It seems to be used as programmable logic.

From the datasheet:

Applications:
• Prototyping/volume production
• Sequential controllers
• Microprogramming
• Hardwired algorithms
• Control store
• Random logic
• Code conversion

- what does the cursor look like, a solid block or an underscore as in my EDIT+ screenshot?

I'm pretty sure you've already checked our Dragon Plus page. I uploaded there a picture of the character set that shows a solid block cursor, but that's based on the data on the eprom chip so I cannot guarantee how it looks until I get the board working.

- can anyone suggest a test to determine whether the extra 64K is being found?

I'll go through the documentation I have and see if there's any test program.

Cheers,
Rob

[admin]

Great to see progress - Phill has a dump of the PROM somewhere and has also done some work reverse engineering how the Plus works in order to fix a real one so may be able to help.

The extra 64K is normally mounted as a RAM disk by FLEX or OS9 - I *think* the command is VINIT or similar.... Just uploaded new VDKs, including the disks with just these drivers on them for OS9.

[robcfg]

It would be nice to check Phill's prom dump and mine to be sure they are ok.

Thanks for the new disk images!

[Pernod70]

This is your new dump of Editor & Assembler:

0007.jpg (35.67 KiB) Viewed 8476 times

0008.jpg (144.78 KiB) Viewed 8476 times

Looks like initialising the virtual disk writes to the wrong area, it' a good test case

[prime]

It would be nice to check Phill's prom dump and mine to be sure they are ok.

Thanks for the new disk images!

I Checked my dump of Simon's prom with another one uploaded here and they where binary identical, was probably yours then Rob, which means we have a good dump......or both dumps are bad in the same way

I did find that when I put Simon's prom in my Plus board that it worked, so I know the prom in my board is knackered Just need to re-implement it in a PLD of some kind to get my board working, don't think an eprom would be fast enough.

I also found that I couldn't get OS/9 to work with the board but got Flex working ok.

I did implement the RAM disk part of the Plus board in MESS a few years back but never implemented the video part, but it's probably got removed over time.

Cheers.

Phill.

[Pernod70]

I also found that I couldn't get OS/9 to work with the board but got Flex working ok.

Good to know it's not just me then.

I did implement the RAM disk part of the Plus board in MESS a few years back but never implemented the video part, but it's probably got removed over time.

There was very little left of the Plus board in MAME, the driver simply had 128K assigned but not used and no sign of the video part. I guess it regressed during modernisation over the years.

The virtual disk now initialises and I can see the RAM being formatted.

0009.jpg (44.72 KiB) Viewed 8462 times

I've no idea about the disk error though. Is there a FLEX manual anywhere?

Anyone know the clock that's feeding the HD6845?