Unfortunately, to put 640 pixels on the screen, even in monochrome at a ~28 kHz sweep rate would mean assuming an 80% active sweep, would still mean writing a byte to the display every 446 ns. While those fast processors that Erik likes would probably be able to do that, IF there was nothing else going on, as well as meeting the other conditions above, it would leave little time to do things such as synchronize with the sweep, fetch the data from elsewhere, manage the grey-scale values in the background, and do the other housekeeping. Of course, this assumes that someone else does all the useful work, since the local MCU won't be having time for any of that.

RE