Close

Revision 6A boards here; work great.

A project log for VDC-II

Commodore 8568-inspired (and mostly compatible) video core for driving VGA-type displays.

samuel-a-falvo-iiSamuel A. Falvo II 01/02/2021 at 07:310 Comments

Just before Christmas, I received the three prototype boards for revision 6A from OSH.  The boards look great, but I wasn't able to construct one until yesterday evening.

Assembly went ... not quite as smoothly as I'd've liked for the first board I tried.  It was a bit colder in the garage than I'd've liked, but the solder hated it more than I did.  While attempting to drag-solder the 74LVC8T245PWR chips onto the board, no matter how much solder I used to flood the pins, it refused to make a clean solder joint.  Wicking the solder just wasn't working well, so I tried to apply a bit more pressure.  While that worked to get the solder hot enough to wick, it also bent the pins of the chips, and ... yeah.  Lesson learned: do not drag-solder when your workspace is cold.

(note the red lines showing where the pins got crushed together.)

After refining my technique to use tack-soldering instead, and making sure to wick excess solder pulling away from the chip instead of trying to sop all the excess in one fell swoop by dragging the wick across the pins, construction went relatively smoothly.  I completed the build of the 2nd prototype card in about six hours.

After fitting a TinyFPGA BX module to the card, I was able to use it as a proper VDC-II card by routing wires over to a breadboard with a resistive DAC on it.

I ran the old clock demo I'd written some time ago, and it runs perfectly.  (A more advanced demonstration which puts the VDC-II into bitmapped graphics mode is still under development as I write this.)

Next steps include:

Discussions