archive.worldofdragon.org

Morning,

Just wanted to say thanks very much for your help and advice, I've finished building the board...
...and to let you know it's working a treat!

Fantastic! That's really good to see

The issue 5 board seems to work fine with standard 18-20pF cyrstals for 4.433619MHz and 14.31818MHz.

The docs for the WDC65C51N say it requires a 1.8432MHz series crystal, with a 1Mohm resistor in parallel, and a 30pF cap to ground, I haven't checked that yet. Is there any serial software for the Dragon I could use to test the serial port?

I was actually going to say, I haven't tested serial yet either - interested in anything you turn up!

You could try the send and receive text options in FastEdit. They are designed for the Dragon 64 (and actually only appear if FastEdit detects a D64 rom signature).

Cheers, I'll give it a try. I think I saw some terminal software in the archive the other day too, but I can't remember where it was.

Next daft question... Does anyone have a spare case and/or keyboard I can buy, so I can complete my new Dragon? I don't really want to sacrifice my original if I don't have to.

Morning,

Just wanted to give an update on the serial comms part of the board, in case it's of help to others building one. I still haven't had chance to test it at the software level as I got distracted playing TeaTime and Chuckie Egg (doh!) but I wanted to post this before too much time passed and I forgot.

The 1.8432MHz series crystal (as recommended on page 19 of the WDC 65c51n document - https://www.westerndesigncenter.com/wdc ... 65c51n.pdf) I used for the serial oscillator of the 65c51n was not working:
So I followed the other instructions on page 19 of the WDC document, and added the 1Mohm resistor, and a 30pF cap to the board like this (sorry for my poor quality soldering):
And after that it looks like this:
I don't have a 6551 from an original D64 to try, so I don't know if this will work for an old chip from a donor board, but I guess then you'd have the original oscillator too, so maybe that wouldn't be a problem?

Good work Sixxie,

I have a broken Dragon 32. It might make sense to rebuild this as a Dragon 64 because I've damaged the original PCB. I could put sockets in for all the chips which would allow me to try the original chips.

Your PCB design might be a good basis for people wanting to extend the Dragon with things like DriveWire or additional internal ROM space.

Hi Sixxie,

I've been trying to get one of Jon's lower case boards working with my issue 5 motherboard but so far I'm not having much luck, as the issue 5 board refuses to start up when the lower case board is connected. The lower case board works fine with my original D32 issue 2, so I don't think there's a problem with that.

I was comparing the original D32 and D64 schematics with the one for the replacement board, to try and work out what might be different, and if I am reading the schematics correctly, the _MS line is tied to _FS on the original schematics, but is connected to +5V on the Issue 5.

When I traced the connections on the lower case board, it doesn't seem to connect to _FS on the motherboard, but it does connect to the motherboard _MS line, and also to both the socket it has for the MC6847, and also to _PE on the 74HCT161 counter the board uses uses to drive some of the address lines for the external character ROM.

So, I *think* (if I am tracing things correctly), the lower case board is passing the _FS signal from the 6847, back to the motherboard via the _MS connection which it is expecting is also tied to _FS, but which is actually tied to +5V on the issue 5 motherboard.

Do you or anyone know if this is likely to be the cause of my non-booting issue 5, which just has some garbage on the screen whenever I power it up with the lower case board attached?

Any help, insight or advice would be very gratefully accepted, I'm currently trying to resist the urge to start tinkering and patching things, when I am not 100% sure I know what I'm doing, as I'll probably get myself into trouble break my motherboard!

Interesting - yes, you'll certainly have hit on the issue there!

My "issue 4" didn't connect MS# at all, as the connection wasn't clear on the scans I'd transcribed from. I fixed mine by bodging it to +5V, as there was no reason in the Dragon's operation for it to ever tristate the address lines (and anyway, I think my DA0 is connected to an HCT logic gate, so I never wanted its inputs to be floating).

But if the lowercase board uses that pin to feed back to FS#, than yep, that's a problem. Annoyingly, it's much easier fixed on my "issue 4" as I can just resolder the bodge wire (and replace that HCT gate with an LS). I'm guessing you'll have to break a track and _then_ solder a bodge

Well, sorry about that... it must be time for an "issue 6"!