DragonPlus Original Board 'Fault'?

For the discussion of all hardware related topics.
Post Reply
dublevay
Posts: 83
Joined: Wed Jan 23, 2019 3:41 pm

DragonPlus Original Board 'Fault'?

Post by dublevay »

Whilst I'm on the subject of the DragonPlus boards, I have also discovered another tiny error that Compusense seemingly made 'back in the day'. The 74HCT165 (IC23) chip which turns the character mappings into 0s and 1s for the screen display has an input called "Serial In" on pin 10. I have noticed that on one obviously quite noisy EPROM I had severe jailbars going down the screen between every character position. Grounding pin 10 completely remedied the fault.

It may be that originally the 74LS165 chips used by Compusense were not as sensitive as the lower power CMOS equivalents - but they probably should have grounded that pin anyway.

The fix is simple, and can be done by adding a link between pins 10 and 15 or pins 10 and 8 of IC23.

I have checked the photos of the original Compusense PCBs, and pin 10 of IC23 is definitely unconnected.
Serenarian
Posts: 22
Joined: Thu Oct 25, 2012 1:28 pm

Re: DragonPlus Original Board 'Fault'?

Post by Serenarian »

I want to thank you for all your hard work deciphering and recreating the DragonPlus board.

I own one of the original Compusense boards. In fact the photo in the archive of a mounted board mounted is my Dragon64.
I was an early Dragon32 and Dragon64 user and wrote a number of articles and presented lectures for the NorthWest TRS-80 User Group.
One of my fellow group members, who was at Salford University at the timee, had a flat in Green Lanes (London) just a few doors away from Compusense. While staying with him I picked up my DragonPlus board, with the Edit+, OS9 and Flex OS9 drivers from Tad. It must have been one of the very first - and it's still working perfectly. In fact it's in the Dragon64 on the desk in front of me now.

Your posting has prompted me to dust off and update a document that I wrote some years ago to provide information to whoever inherits my computers. It goes into some depth about the DragonPlus and 6845 so may be of use to people who have one of your boards - or for anyone who is curious about its capabilities.

Feel free to distribute it.
COMPUSENSE DRAGON PLUS BOARD.zip
(141.77 KiB) Downloaded 78 times

Peter Mooney
MaestroSoftware
Posts: 24
Joined: Wed Jan 01, 2014 6:59 pm

Re: DragonPlus Original Board 'Fault'?

Post by MaestroSoftware »

Hey Peter,

That's an incredibly detailed document. If I had had an EPROM programmer and this very clear document, I surely would have accomplished my teenage dream : a real WYSIWYG word processor for the DragonPlus with French (accented) characters. I gave up trying to do that because I couldn't understand the format of the character set EPROM. I will now play with the emulators and possibly get my hands on an EPROM programmer to experiment with that.
And all the rest of the document is similarly explicit ! Thanks a lot

(I wonder how many original Dragonplus boards are still working - my memory extension is still working but I have to fix the monitor connections that got unsoldered over the years) - when https://worldofdragon.org/index.php?tit ... ors_Corner was written, apparently there were only 5 non-functional Dragonplus boards known to the author.

Philippe
Post Reply