V3: Enter the improvements

This is the formal release of version 3 of the board. In fact, while the board has been out in the wild for literally years by now (and I'm actually ready to release V4), a formal release was still missing. I'm sorry for that, I just forgot to do it and never noticed. There are no changes, this formal release is exactly the same stuff that has been on the master branch for the last, erm, three years.

In this release we started making serious improvements to the board. The reasoning behind every modification is detailed on the Development Blog, so I'll be pretty terse here.

• Switched to external power regulation, using the C64 power circuit and power supply: drastically reduces the heat inside the case, which is one of the main CPU/TED failure causes.
• Added current-limiting resistors on all ports exposing power pins: this will avoid short-circuiting the power supply, whatever you do on the external connectors.
• Added internal Joystick port buffers: this is basically like having two OpenC16JoyAdapters built into the machine, preventing the TED pins to be directly exposed on the joystick ports, which is another common cause of TED failures. It also gives the ports a fixed ground, allowing the use of "advanced" joysticks with autofire functionalities for instance, which require power from the machine.
• Joystick ports now use DB-9 (more properly: DE-9) connectors, just like any other machine of the era: you can now use your favourite C64/Amiga joystick on your C16.
• Similarly, the Datassette port was changed to the C64-style edge connector. An adapter to keep connecting the 1531 Datassette is trivial to make.
• Moved to the C64 power switch, since this can still be found on the market and is functionally equivalent.
• The CPU can now either be an original 7501/8501 or even a 6510, thanks to Andrew Challis's adapter being integrated on the board.
• In a similar fashion, the board can either directly accept an original MOS 251641 PLA or Daniël Mantione's GAL16V8-based reimplementation.
• The design flaw that prevented the usage of cartridge-based RAM expansions was fixed: you can now plug in an OpenC16RamExpansion without the internal RAM fighting with it.
• Actually that might not even be necessary, as the board now directly supports either 16 or 64 kB of internal RAM.
• Since the RF modulator is basically useless these days, a replacement circuit was integrated on the board, providing either Luma+Chroma (say S-Video) or Composite Video.
• Added the possibility of combining the KERNAL and BASIC in a single all-in-one ROM: this allows replacing the original power-hungry chips with a single W27C512, which can also incorporate the Plus/4 function ROMs.
• ESD protection was improved on all ports.
• The track and ground plane layout were optimized in a few places in order to reduce noise and crosstalk.

While the comprehensive switch of connectors to the C64 counterparts might be frowned upon, it was done because C64-style cases are still in production and this way LittleSixteen V3 will fit them just perfectly, yielding the ability to build new C16s from scratch, which is another one of our goals.

Be sure to read the assembly notes carefully and enjoy!

Released files

Note that the released gerber files are password-protected. The original reason behind my projects was to allow anyone to make their own retrocomputing accessories cheaply. Instead of this, what I achieved was actually fuelling greedy people grabbing my work, making boards for a couple of bucks and the selling them at outrageous prices ($15 for a badly-soldered OpenC64Cart that costs $2 to make is just ridiculous).

I still believe in free software and open hardware, and that is why my projects will remain as such. I am no longer providing ready-to-use gerber files, but you can still generate them from the KiCad project or ask me for the password, if you think you don't fit the above statement.

If all you want is to get boards made, I would really appreciate if you did it as explained in the Support section in order to get them cheaply while supporting the project.

Note that you are NOT allowed to use these boards commercially, but I won't care if you sell them AT COST. Let me repeat that: AT COST.

V2: Enter the PCB!

In the hope to improve the schematics, I laid out the pcb, using an original rev. B board for reference. This sort of validates the schematics, which should be 100% correct now.

Some notes about this release:

• The original board was probably laid out by hand and a lot of tracks were drawn with arbitrary slopes. I have sticked to only 45 degrees tracks, which of course means I could not follow the original tracks exactly, but I tried to stay as close to them as possible and to keep all the "visual hints" that allow identifying a track quickly. I must admit I'm quite satisfied of the end result, to be honest.
• I used my usual track widths and via sizes (plus some new values for the larger tracks), I didn't bother figuring out what sizes the original board used.
• All tracks were laid out "by eye", which means with reasonable - not maniacal - accuracy to the original design. Most care was taken in the positioning of components that ought to be in a certain position (i.e.: screw holes and I/O connectors), to ensure drop-in replaceability. Other components and tracks are "more or less" there, but as the board was wholly laid out from scratch by hand, don't expect sub-millimeter accuracy.
• The footprints for all DIP chips use "long pads". This makes them easier to solder and more solid to the board should you need to rework them. This forced a few tracks running very close to the original pads to be slightly offset away.
• Some footprints are slightly longer/larger/wider pitch/whatever than the originals, so that I could use ready-made KiCad libraries.
• Footprints for the connectors and modulator were taken from StormTrooper's Plus/4 remake, without checking them for correctness.
• I didn't bother to create the right footprint for the original power connector, as there's no point in wasting time for some item that is nowhere to be found these days. I used a much more common one instead. Same goes for the inductor.
• I didn't pay much attention to the silkscreen, many labels can probably be placed better, but I added a description for every IC, like it or not.
• Proper footprints were added for all the protection diodes that Commodore forcibly retrofitted on real boards (See D96-99).
• With the C16, Commodore went as far as saving a few cents by not mounting the decoupling capacitors for a few chips. They left the pads on the board but removed all silkscreen indications. These were restored and assigned random numbers.
• The ground fill is autogenerated by KiCad, so it won't match the original exactly (not even close).
• Probably there's something more I've forgotten.

Of course nothing was tested, so errors might still be there.

Use at your own risk.

Please note that the license changes to CC BY-NC-SA 4.0 with this release, which means that any commercial use is now prohibited.

First release

This release contains only the schematics, which might contain errors.

Use at your own risk.