Dragon 200E Lower Case Daughterboard ROM question

[tjewell]

I'll second that, I have one in one of my Dragons here and it works great.

[Go4Retro]

John put some secret data in his own font files: https://www.go4retro.com/2024/11/16/exp ... ts-part-2/

[Go4Retro]

It works!

https://www.go4retro.com/2024/11/17/exp ... ce-part-2/

[robcfg]

Very nice!

It's also good that you managed to reduce the board size.

If the eprom could be changed by one in PLCC package and the rest of the components rearranged, maybe we could get two boards in a single 100x100 pcb thus helping reduce the price.

Congratulations!

[dublevay]

Hi Jim,

Sorry - I have been busy on other things. I have conquered the file once, but every time I look at it again it confuses me. I view the file in a hex editor, 256 bytes wide, so that each character can then be read downwards over 12 rows. You then get 2 sets of 128 characters in each 12 rows. It's been a while since I used it though.

I do have two boards left, but am out of the HCT245 and HCT161. I will likely re-stock, as it has been a popular board, but I might take your lead and reduce the board size further, especially as there was a teensy weensy little fault with the board which required the fitting of one capacitor backwards (I'd not found KiCad's board error checking facility properly at that time! ). Rob's idea of the PLCC EPROM is nice - although that said, I do have loads of DIP28 ones to get through! I've never really explored the board panels option, I must admit. I just design the board as I see fit, then get however many I want produced. Unless I opted for the PLCC, I probably couldn't get much smaller than your design, even with the supporting logic as SMD.

I'm afraid you completely lost me with this bit... "I made one “executive” decision on this update, which I am sure will anger some purists. While having free space all self contained in spot of the ROM, I don’t see any useful value for it beyond stowing some explanatory text or copyright, and it makes understanding the ROM data much more difficult. So, I placed the 4 counter address lines at the bottom, meaning each font glyph bitmap will occupy 16 consecutive addresses in the EPROM. Since the files will be Open Source, others can revert that change if it offends them."

Cheers

John

[Go4Retro]

Very nice!

It's also good that you managed to reduce the board size.

If the eprom could be changed by one in PLCC package and the rest of the components rearranged, maybe we could get two boards in a single 100x100 pcb thus helping reduce the price.

Congratulations!

Actually, you can now, as one of the dimensions is 49.5mm:

Dragon_LowerCase_v1 PCB.png (49.97 KiB) Viewed 37620 times

But yes, another design I have is ~100x22mm, so at least 3 could be made on the same PCB (EPROM is PLCC, all ttl is SMT) Not sure how small the PCB needs to be, though.

[Go4Retro]

Hi Jim,

Sorry - I have been busy on other things. I have conquered the file once, but every time I look at it again it confuses me. I view the file in a hex editor, 256 bytes wide, so that each character can then be read downwards over 12 rows. You then get 2 sets of 128 characters in each 12 rows. It's been a while since I used it though.

Yep, it took me a bit, but I grokked it eventually

I do have two boards left, but am out of the HCT245 and HCT161. I will likely re-stock, as it has been a popular board, but I might take your lead and reduce the board size further, especially as there was a teensy weensy little fault with the board which required the fitting of one capacitor backwards (I'd not found KiCad's board error checking facility properly at that time! ). Rob's idea of the PLCC EPROM is nice - although that said, I do have loads of DIP28 ones to get through! I've never really explored the board panels option, I must admit. I just design the board as I see fit, then get however many I want produced. Unless I opted for the PLCC, I probably couldn't get much smaller than your design, even with the supporting logic as SMD.

Feel free to use it. I'll put the gerbers and the open source logo on it and push a new version

I'm afraid you completely lost me with this bit... "I made one “executive” decision on this update, which I am sure will anger some purists. While having free space all self contained in spot of the ROM, I don’t see any useful value for it beyond stowing some explanatory text or copyright, and it makes understanding the ROM data much more difficult. So, I placed the 4 counter address lines at the bottom, meaning each font glyph bitmap will occupy 16 consecutive addresses in the EPROM. Since the files will be Open Source, others can revert that change if it offends them."

Cheers

John

I rearranged the ROM contents to instead of the data being:

<$000> First byte of character
<$100> second byte of character
...
<$b00> 12th byte of character
<$c00-$fff> free space

My EPROM looks like:
<$000> first byte of character
<$001> second byte of character
...
<$00b> 12th byte of character
<$00c> free byte
<$00d> free byte
<$00e> free byte
<$00f> free byte
<$010> first byte of second character
<$011> second byte of second character
...

It made composing ROMs easier (you can just add a ROM by concatenating it onto the binary, no regard for making them sets of 2 fonts first), it made the ROM easier to understand (in your case, you can just look at the hex in 16 byte chunks and each line is a character bitmap and 4 blank bytes), and layout was marginally easier as well.

jim

[dublevay]

Have you changed the EPROM addressing then? Because surely the 6847 expects to find the character data in a specific format? I cannot remember how it works, but there is a special key combination on the Dragon 200E which switches between the normal and special character set - and it can also be done programmatically. Will that still work?

[dublevay]

Feel free to use it. I'll put the gerbers and the open source logo on it and push a new version

Definitely won't just copy it - would be a re-work of my own.

[dublevay]

Have you changed the EPROM addressing then? Because surely the 6847 expects to find the character data in a specific format? I cannot remember how it works, but there is a special key combination on the Dragon 200E which switches between the normal and special character set - and it can also be done programmatically. Will that still work?

Oh, I see - you flipped round the row and DD address lines to the EPROM.