Retro Games THEC64 User Manual page 109

Un-shifted display (PAL C64) Vertical Shift +12 (PAL C64)
On THEC64, you can adjust the vertical position up or down using values of -15
(moving the main central area down) to +17 (moving the area up) for a C64, -16 to
+16 for VIC 20 PAL, or -13 to 0 for VIC 20 NTSC, by adding this to a CJM text file.
However, using the vertical shift value on a program running on an NTSC C64
computer can cause a problem if you have a vertical shift value of more than +6 in
your CJM file. You are likely to see odd graphical issues appearing in the bottom few
lines of the display as you reveal an area that is beyond the NTSC C64's border. For
this reason, not many NTSC C64 programs use the borders and if they do, they tend
to only use a few of the lines in the border area.
See CHAPTER 7 for further details on all of the options and settings. See
CHAPTER 8 for further details about filename flags and CJM files.
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