Video Signal Generator Owner's And Programmer's Manual

6-56 Chapter 6: Programming
Model 801GC, 801GF & 801GX¥Rev. A
The frame rate is equal to HRAT divided by VTOT.
This should match the frame rate given on your spec
sheet.
Active Video Physical Size
The USIZ, HSIZ and VSIZ parameters do not affect
the sync timing or signal outputs of the 801G*. They
do, however, greatly affect the test images that are
drawn. For example, the size of the box in the “Bright-
ness” test pattern should match the size of your light
meter probe. The actual size of the probe is entered
using the system parameter MSIZ. The firmware com-
bines this information along with the format’s physi-
cal size information to properly scale the size of the
box. The firmware also uses the format’s size infor-
mation to make sure the crosshatch lines in the SMPTE
RP-133 pattern form square boxes and that the circle
is round and not elliptical.
The USIZ parameter determines whether the unit of
measure will be interpreted as inches (1) or in mm
(2).
The HSIZ parameter is the horizontal width of the
active video area on a properly adjusted display.
The VSIZ parameter is the vertical height of the active
video area on a properly adjusted display.
❖ Changing the values of HSIZ and (or) VSIZ will
not change the overall size of most test images
on your display.
Display Codes
Many video controller cards for the Apple Macin-
tosh II and VGA type cards for the IBM-PC are able
to identify the type of display connected to them by
checking one or more display code sense lines com-
ing from the display. The information is then used
to select one of several different operating modes to
match the display. An improper display code may
make the controller card or display appear to be