It's actually simpler than a table of voltages. It's a series of trinary values that indicate whether to use positive, negative or zero voltage. The actual voltage used is static (even the specialized EPDC PMIC (which _is_ a separate chip) doesn't allow changing it on the devices I've seen). The waveform (as they call the lookup table) is sometimes actually stored on a separate flash chip soldered on to the display's built-in cable. Years ago I wrote a tool to decode and convert the proprietary formats used by the E Ink corporation for these: https://github.com/fread-ink/inkwave