Int 10 Fn 12  - Tseng Et-4000 Bios - Get/set Screen Refresh Rate           [V]

   AH = 12h
   BL = F1h
   AL = subfunction
       00h set refresh rate
       01h get refresh rate
   BH = video mode
       00h  640x480
       01h  800x600
       02h  1024x768
       03h  1280x1024
   CX = new refresh rate (see #0033) if AL = 00h

Return: AL = 12h if supported
       CX = current rate (for AL=00h, a changed CX indicates failure)

(Table 0033)
Values for Tseng ET4000 refresh rate:
 CX    640x480 800x600   1024x768/1280x1024
 00h   60 Hz    56 Hz     interlaced
 01h   72 Hz    60 Hz     60 Hz
 02h   75 Hz    72 Hz     70 Hz
 03h   90 Hz    75 Hz     75 Hz
 04h   --   90 Hz     --