*Bits 1..0 define the interlace mode.
==== Interlace sync mode (ISM) ====
In this mode, the same information is painted in both fields to enhance readability. Reprogramming the CRTC is not necessary.
==== Interlace sync and video mode (IVM) ====
In this mode, alternating lines are displayed in the even and odd field to double the resolution.
On the even frame, the CRTC displays the lines for which VLC is even. On the odd frame, the CRTC displays the lines for which VLC is odd.
In this mode, it is necessary to reprogram the CRTC as if we were building a frame of 624 lines. The 625th line is managed automatically by the CRTC.
2 interlace modes are available:
* In interlace sync mode, the same information is painted in both fields to enhance readability. In this mode, reprogramming the CRTC is not necessary
* In interlace sync and video mode, alternating lines are displayed in the even and odd field to double the resolution. In this mode, it is necessary to reprogram the CRTC as if we were building a frame of 624 lines. The 625th line is managed automatically by the CRTC
[[File:CRTC Interlace modes.png]]