[[File:CRTC Interlace modes.png]]
=== UM6845R and R31 on Type 1 ===
R31 is described in the UM6845R documentation as "Dummy Register".
R31 doesn't exist on types 0,2,3,4.
=== UM6845R and R12/R13 on Type 1 ===
The UM6845R differs to other CRTC in respect of R12/R13.
In demos to make a display compatible with all CRTCs, program R12/R13 when VCC!=0. This will then take effect at the next frame start.
=== UM6845R status Status register on Type 1 ===
The UM6845R has a status register that can be read using port &BExx.