As revision 3 and the control module for it was received mostly with praise, I decided to revisit DD2 once again and do possibly the last upgrade of the DolphinDOS 2 line. Things on my TODO list were:
  • group all the jumpers again, so that the last-minute addition to Revision 3, namely the selection of an additional DOS can be done from within the same jumper block as everything else
  • integrate the surprisingly popular (more than I expected it to be) — especially among the SX-64 folks — control module as an optional block onto the main board
  • deal with the over-pending reorientation of the parallel connector so that all regular sockets and connectors could be used without additional efforts related to the orientation of the key notch
Here is the result. Revision 4 fixes all of the above, while keeping the compatibility with Revision 3 control module. In other words if you have a Rev.3 control module, you can use it with Rev.4 board. Having said that — if you want to have three DOS versions being selectable with the control button, you need to use the on-board block as the Rev.3 module doesn't handle more than two DOSes.






  1. The optional components are marked with a dashed rectangle. If you don't need/want the control circuit, you don't need to load the components enclosed within that rectangle.
  2. ID pins (JP1 7-8, 9-10) have to be both CLOSED or you will get your device working as drive 11 rather than - what you probably expect - 8! This is of course important only if you don't use the optional control circuit, which otherwise takes care of the selections. In such case you don't use any jumpers on the jumper block.
  3. CON4-0 and CON4-1 are 20-pin pinheads, which I use for connecting to the main controller board’s 6502 soldering pads. CON3-0 and CON3-1 do the same for the 6522 VIA. I use "goldpin" type of connectors for them. If you plan to use the same, please note that the pins need to be kept straight when mounting. I myself use socket constructions to keep the strips straight and aligned when soldering. For this revision I dropped the idea of reduced drills diameters I used in the previous revision. It worked well for me and most of the others but not for everyone.
  4. Care has to be taken when mounting the hardware inside the drive in order to make it sit low and fit properly inside the drive’s case, yet remain elevated above the level of other elements on the controller’s main board!


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