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The VTOT parameter sets the total number of hori-
zontal scan lines, active + blanked, in one complete
frame. It must be an odd number when SCAN = 2.
If your spec sheet gives you the frame period in
units of lines, use this value for VTOT. Here are
some ways to calculate the value for VTOT from
other data on your spec sheet:
• A spec sheet may give you the number of
horizontal active and blanked lines per frame
as two separate numbers. Add the two num-
bers to get VTOT.
• A spec sheet for a non-interlaced display may
give you a vertical rate. The value for VTOT
can be calculated using the following formula:
VTOT = HRAT / Vertical Rate
• A spec sheet for an interlaced display may give
you a field or frame rate. The value for VTOT
can be calculated using one of the following
formulas:
VTOT = HRAT / Frame Rate
VTOT = 2 x (HRAT / Field Rate)
• A spec sheet for an interlaced display may give
you the number of active and blanked lines in
a single field. The value for VTOT can be cal-
culated using the following formula:
VTOT = 2 x (Active Lines + Blanked Lines)
The VSPD parameter sets the number of scan lines
between the last line of active video and the begin-
ning of the vertical sync pulse. Many spec sheets
refer to this parameter as “Vertical Sync Front Porch.”
If your spec sheet gives you the vertical front porch
in units of lines, use this value for VSPD. Here is
another way to calculate the value for HSPD from
other data on your spec sheet: