Sunday, 26 April 2015

V9938 with RGB output

With the 9129 it's possible to write with maximum speed to VRAM if the screen is off.
This is not possible with the V9938. I don't know why? - I have to take a look in the datasheet.
Now I write with some NOP's to VRAM and it works...

After I viewed some old philips MSX2 schematics I built these emitter followers at the V9938 outputs.
Modifications to VG8235:
- NPN-transistor for the csync-signal with 1k basis-resistor and 220 ohm emitter resistor.
- I changed the R,G,B emitter resistors from 100 to 220 ohms.
-> This works fine with my 1084s. It has 150 ohms input resistors. Most TV's have 75 ohm input resistors. There it should work too.
Maybe this doesn't work with all monitors / TV's, but I have a perfect picture :-)

In the SCART-connector you have to connect CSYNC to pin 16 and pin 20!


  1. Hi.

    Will these be available to buy (either as kit or pre-built) ? And if so when ?


  2. No, I don't want to sell my LC64 ;-)
    When the PCB desgin is finished you can get the layout for free.
    It's possible that I order some more PCBs...
    But some chips are not easy to buy!