I think this is correct:
For moving graphics on the ZX80 you needed to output directly from the CPU, via an I/O port, to the display, as the CRT electron beam scanned across.
On high end luxury hard...
@nprofile1q... This brings the nostalgia of CGA programming, with the writes to the video buffer that had to be timed using PIT to corrspond to the CRT blanking intervals. You had to do the writes when the electron beam was invisibly going back after finishing a line or a frame, otherwise you'd see snow on your screen.