Ah, shades. Well, the intensity of the colors are different between the C128 and CGA.
Yes, the difference beetween the unintensified and intensified colors can be different in the Commodore monitors, and that is because the contrast potentiometer in the IBM monitor only acts over the unintensified colors.
The input RGBI color processing in the Commodore 1902 monitor is the same as the IBM-5153 and will give four levels of intensity like the IBM monitor does.
You can be comfortable with the color range found on almost six resistors network dacs, but if you want the whole range of intensity colors, you need something more.
I am glad that there is more interest in the 128 and specifically the VDC output. That was my goal when I started making my first adapter. I want everybody to be using the 128 in 128 mode with 80 col software.
Your design looks extremely well done! It would be great if you could share some details about the circuit design and what you put in and why.
The circuit has no secrets:
One 74541 as a input buffer (better to route than the 74244 because the inputs and outputs are face to face)
Two plds ATF16V8 because I already have the programmer and some of them.
The resistors network.
One video op-amp LMH-6722 working as a output buffer.
Two 500K potentiometer to adjust the svideo luma and chroma lines.
One 3.5mm for the audio output.
One 3.5mm NC jack (normally closed) for the audio input. The audio input is grounded when the jack connector is unplugged.
Two capacitors oriented to the sid serving as protection when the audio jacks are plugged or unplugged.
One 5v supply connector.
Do you want the eagle and pld files ? Send me a PM and I will send it.
Because that is what the VDC 80 column output USES.
If you don't want CGA then you don't want 80 column.
Right. The commodore 1902 monitor works in the same way. I simulated the IBM-5153 conversion circuit and I can confirm that the final transistors yields four different intensity levels but with the black above zero.
Sorry. I forgot to explain what the connectors are:
DSUB 9 for the RGBI input from the C128. DIN 5 for the audio/video input from the C128/C64.
Mini din 4 connector for the svideo output, and input to the Framemeister XRGB mini (Chroma and luma lines pass throught a 500 k pot). Mini din 8 connector for the RGB output, and input to the Framemeister XRGB-mini. Jack 3,5 mm for the audio. Jack 3,5 mm for the audio out.
The voltages data table clearly shows that there are four different intensified color levels:
One color intensified alone.
Two colors intensified together.
Three colors intensified together.
All intensified color voltages are always fixed because them not change with the contrast level potentiometer. Because in the table the unintensified colors are set at the maximum level I preferred adjust them at 0.85V instead 1V.
To implement all these a lot of logic IC and resistors would be needed, then the pld is the best choice.
And this is the result, with the output voltage values exactly like the table (at the input of the operational video amplifier instead the input of the gun amplifiers).