I can tell for sure it is
pin-compatible and likely
was "redesigned by looking at horizontal and vertical microsections / micrographs" (a standard technique employed in the GDR and mastered to perfection).
(no first hand info, quote from related Robotron pages)
- U82720 DC04 (8,34 Mhz @ VIS3
- less than 4 MHz clock: U82720 DC03 and DC02
U82720 veb mikroelektronik / Robotron (198x)U82720 from Robotron (PDF in question)Raw TIFs suited for OCRVIS3
graphics card (GDR 19??)VIS3 Beschreibung und Treiber (DOC)
The VIS3 package (above) contains lots of drivers and good documentation. Even the 4 plane mode (known from the Rainbow) is described...