Documentation for color reprogramming

README.md

@@ -1,6 +1,6 @@
 # C64 Video Enhancement
 
-FPGA based modification board for the Commodore 64 computer to produce YPbPr video output.
+FPGA based modification board for the Commodore 64 computer to produce YPbPr or RGB video output.
 
 The C64 is the most iconic device of the 8-bit computer era and there is a huge library of
 software and hardware modifications available.
@@ -156,9 +156,50 @@ saturation as a whole, you can replace the resistors R18 and R19 with lower valu
 well solder an additional 150 Ohm right on top of each of the existing R18 and R19 (this also results
 in 75 Ohm total). 
 
-I am already planning future versions of the firmware, where you can configure each palette color 
-independently in software. But this may take some more time.
-
+Beginning with firmware version 2.0, you have the possibility to freely choose a color palette that
+suits your taste. It is even possible to reporgram the color signals to produce RGsB or RGB signals instead
+of YPbPr. When you choose to disable sync, you need to get the sync signal from the original A/V port instead.
+In this case it is even possible to build an adapter cable that joins the A/V signals and the RGB signals
+together to a single SCART connector.
+
+## Details on color signal reprogramming
+Beginning with firmware 2.0, the mod uses a set of 256 16-bit registers to hold the palette information.
+These registers can be reprogrammed directly from the C64 and stored persistenly on the FPGA chip.
+### Unlock the registers
+Before you can change the register contents, you need to write a value of 137 to memory address 53311.
+Then switch the output mode switch to a different mode and back again (back is optional). This sequence is 
+necessary to prevent untrusted code to modify the settings. This could a be a special concern on demo competitions.
+### Write into registers
+For writing a 16-bit value, you need to first write the low byte into address 53308 and the high byte
+into address 53309. Then write the target register number into address 53310. You can store the same value
+into multiple registers by writing additional register numbers into 53310 without changing the data each time.
+Note that it is not possible to read out any register contents. 
+### Store permanently
+When you have changed the registers to your liking, you can store this permanently by writing the value 138
+to address 53311. During storing this will also cause some random pixels to appear on the screen for a short time. 
+### Meaning of the registers
+The registers can be thought of to form a 16x16 matrix (stored line by line), where each cell specifies the exact color
+that needs to be produced when the computer wants to display one of its 16 colors, with the consideration
+of which color has been displayed in the line directly above. 
+
+If you do not want to simulate PAL color blending, all rows in the matrix will hold the same value. 
+There it does not matter for the current line, which color has been displayed above. 
+
+If you want to do color blending, you can cook up any coloring blending 
+scheme you want. The register accessed is always defined by currentcolor * 16 + colorabove. 
+
+Each register contains 3 5-bit numbers that specifiy the analog signal levels to be sent on the signal outputs.
+| Bits  | Signal   |
+|-------|----------|
+| 0-4   | Pr       |
+| 5-9   | Pb       |
+| 10-14 | Y        |
+| 15    | unused   |
+### Disabling sync 
+Bit 15 of register 0 has a special function, as it can be used to suppress the sync signal.
+Writing a 1 into this bit will turn off sync on the Y line, when the 240p/288p output mode is selected.
+In this mode, the luminousity line of the original A/V connector can be used to get a sync signal from
+instead. 
 
 ## Contact
 For technical questions and also to share your experience with this modification, please