200E ROMs

A place to discuss everything Dragon related that doesn't fall into the other categories.
dublevay
Posts: 38
Joined: Wed Jan 23, 2019 3:41 pm

200E ROMs

Post by dublevay » Tue Jan 29, 2019 11:09 pm

I've successfully reproduced the 200E VDG daughterboard, and wanted to try it out with the 200E 'firmware'. So I've flashed IC18/IC34 and replaced it on the motherboard. I've also done IC17/IC37, but I don't think that is important unless doing an EXEC48000?

For some reason, despite trying a few different EPROMs, the 200E BASIC ROM doesn't want to boot. I just get a type of 'no ROM' pattern on the screen.

Any ideas why the 200E ROM might not run? I was under the impression that the base hardware was identical?

dublevay
Posts: 38
Joined: Wed Jan 23, 2019 3:41 pm

Re: 200E ROMs

Post by dublevay » Tue Jan 29, 2019 11:20 pm

Hmmm..I think I realise what I've done. I've been using 2764s! It should be 27128s. D'oh.

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robcfg
Posts: 1221
Joined: Sat Apr 04, 2009 10:16 pm
Location: Stockholm, Sweden

Re: 200E ROMs

Post by robcfg » Tue Jan 29, 2019 11:25 pm

Definitely the same hardware. Check the board scans here.

Can you post pictures of your daughterboard?

Which kind of eprom are you using? And most important, did you do the layout of the board to be compatible with regular 27xx eproms? Because the original daughterboard has a 2532 eprom chip which is not compatible with the usual 2732 and alike.

dublevay
Posts: 38
Joined: Wed Jan 23, 2019 3:41 pm

Re: 200E ROMs

Post by dublevay » Tue Jan 29, 2019 11:28 pm

Hi,

Yes, the daughterboard is fine - works absolutely perfectly. Was just having trouble with the ROM, but have just blown another so back off upstairs to try it out! :)

John

dublevay
Posts: 38
Joined: Wed Jan 23, 2019 3:41 pm

Re: 200E ROMs

Post by dublevay » Tue Jan 29, 2019 11:37 pm

Now works just fine. Here is the daughterboard.
Daughterboard.jpg
Daughterboard.jpg (813.12 KiB) Viewed 826 times

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robcfg
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Joined: Sat Apr 04, 2009 10:16 pm
Location: Stockholm, Sweden

Re: 200E ROMs

Post by robcfg » Tue Jan 29, 2019 11:42 pm

Excellent job!

Are you planning on doing some boards, because I'd like one. If making a kit or offering a fully assembled one is not on your plans, I could do with a bare board.

dublevay
Posts: 38
Joined: Wed Jan 23, 2019 3:41 pm

Re: 200E ROMs

Post by dublevay » Tue Jan 29, 2019 11:51 pm

I just want to make some refinements to the boards (moving the jumper slightly left and increasing the VDG pin holes so I can fit a ZIFF socket to test 6847s). Then I will order some more.

I plan to offer bare boards and fully built - but haven't priced anything up yet. No doubt I will get caught for import VAT and fees when ordering more boards! :)

I also need to work out whether these will coexist with my DragonPlus boards - not sure how long the legs can go on those!

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robcfg
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Location: Stockholm, Sweden

Re: 200E ROMs

Post by robcfg » Wed Jan 30, 2019 8:37 am

Nice! Please keep us posted!

dublevay
Posts: 38
Joined: Wed Jan 23, 2019 3:41 pm

Re: 200E ROMs

Post by dublevay » Sat Feb 09, 2019 12:44 am

I've now posted these in the for sale section. I will be offering them to the Facebook group tomorrow (they got first dibs on the first four - and they went rather quickly!)

dublevay
Posts: 38
Joined: Wed Jan 23, 2019 3:41 pm

Re: 200E ROMs

Post by dublevay » Wed Feb 13, 2019 1:03 am

Have now spent a bit of time decoding the character EPROM. Basically, if the ROM content is viewed as 256 column width, then the 12 byte characters can be read downwards in something like FRHED.

I've also discovered that by pulling pin 1 of the EPROM high, a secondary character set is present, which still retains the nicer styled font, but brings back the old inverse characters.

Pin 1 of the EPROM can be pulled high by connecting it to pin 24 of the same chip via a 100 ohm resistor, rather than connected directly.

If I make any newer versions of the board, then this mod will of course be incorporated, but it should be a simple modification for anyone so inclined to make to the existing boards.

And actually, thinking about it some more, as pin 1 is controlled from INTEXT directly from the motherboard, it must be possible to access this secondary character set programmatically from the Dragon. I wonder if the 200E ROM has another way to select it?

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