I just reminded myself that I got two UM6559, bought few years ago (unfortunatelly, only this DAC, no PPU)
After some testing I can say that:
* Both VCC pins (3, 15) are shorted internally
* GND pins are not shorted internally
* pin 7 (NC) seems to be unknown input (internally wired)
* pin 13 (NC) seems to be unknown output - it toggles after 3rd, 5th and 8th falling edge of clock, generating alternating pattern (05.png):
* RED, GREEN, BLUE: 8 levels (non-loaded): 0.95V, 1.18V, 1.42V, 1.65V, 1.89V, 2.12V, 2.35V, 2.60V
* SYNC: 2 levels: 0V, 5V
* LUMA: 5 levels (non-loaded): 1.15V, 1.97V, 2.43V, 3.03V, 3.41V
* SYNC = inverted CD6
* RED/GREEN/BLUE/LUMA are output only if CD6 is low
POWER UP condition:
* SYNC line works immediatelly since first clock cycle
* RED/GREEN/BLUE works after around 132 clock cycles
Transition:
After setting value on CD0..CD7, there need to be at least 8 edges of clk.
* RED/GREEN/BLUE changes on 5th falling edge
* LUMA changes on 8th falling edge
Exact values of RED/GREEN/BLUE for all CD0..CD5 combinations:
RED: 0,0,5,2,0,0,4,6,2,2,6,6,1,0,2,5,3,3,7,5,0,0,6,7,4,4,7,7,2,0,5,7,5,2,5,2,4,6,4,6,6,6,6,6,2,5,2,5,7,5,7,5,6,7,6,7,7,7,7,7,5,7,5,7
GRN: 0,0,5,6,2,2,6,6,1,0,2,2,0,0,4,5,3,3,7,7,4,4,7,7,2,0,4,4,0,0,6,7,5,6,5,6,6,6,6,6,2,2,2,2,4,5,4,5,7,7,7,7,7,7,7,7,5,5,5,5,6,7,6,7
BLU: 0,0,5,6,1,0,2,2,0,0,4,6,2,2,6,5,3,3,7,7,2,0,5,5,0,0,6,7,4,4,7,7,5,6,5,6,2,2,2,2,4,6,4,6,6,5,6,5,7,7,7,7,5,5,5,5,6,7,6,7,7,7,7,7