Alternate firmware for ZXKIT1 VGA scandoubler for ZX Spectrum

PCB: https://github.com/romychs/RGB2VGA

• Low delay (one line)
• Automatically adjust to input timings
• Automatically detect input VSYNC(KSI), HSYNC(SSI) polarity. Supported schemes: V+ H+ and V- H-
• Support for CSYNC (composite sync) input (should be connected to SSI input, KSI should be pulled hight)

Jumpers:

• INVERSE_RGBI - changes polarity of input RGBI signals
• INVERSE_KSI - changes polarity of output VSYNC signal
• INVERSE_SSI - changes polarity of output HSYNC signal
• INVERSE_F14MHZ - changes edge of clock to latch input RGBI signal
• VGA_SCART - no effect
• SET_FK_IN - no effect
• SET_FK_OUT - no effect

PCB modification: to get this firmware working you need to bridge CPLD pin 90 and pin 83.