3 ms·
IIRC flicker free depends on NMI from the ULA eg see > The ULA contains a 6.5 MHz crystal oscillator and a frequency divider which generates horizontal sync pu
by klelatti 4y ago
IIRC flicker free depends on NMI from the ULA eg see
> The ULA contains a 6.5 MHz crystal oscillator and a frequency divider which generates horizontal sync pulses at the video output and NMI pulses on the NMI output.
From
https://8bit-museum.de/heimcomputer-2/sinclair/sinclair-scans/scans-zx81-video-display-system/ https://8bit-museum.de/heimcomputer-2/sinclair/sinclair-scan...