GETSCANLINE

Compatible with:
DOS Maximite CMM MM150 MM170 MM+ MMX Picromite ArmiteL4 Armite F4 ArmiteH7 CMM2

Syntax:
GETSCANLINE

Description:
This will report on the line that is currently being drawn on the VGA monitor. 
Using this to time updates to the screen can avoid timing effects caused by updates while the screen is being updated.

GETSCANLINE zero is always the start of the first visible line.

The maximum value returned for each mode varies depending on the mode..
The table below contains the maximum value returned by GETSCANLINE for each mode.
Finally it lists the time in microseconds for the time between the end of the last line and the start of the first line.

Most mode take between 20 and 30 uS per line so something like
IF GETSCANLINE = MM.VRES might take a few video frames before triggering.
You need to allow a range of values to be sure that your code will see the value at the earliest opportunity..
IF GETSCANLINE > MM.VRES and GETSCANLINE < (MM.VRES+5)
is a safer way to initialise an action and will work for all modes.

When you set a MODE, you can specify a subroutine that gets called at the start of the blanking period.
This if often a simpler way of doing things during blanking.

 
            GETSCANLINES
mode   display    maximum      uS of
       lines    scan lines   blanking
1       600        627         750
2       400        499        2690
3       200        249        2690
4       432        499        1800
5       216        249        1800
6       240        249         540
7       240        249         540
8       480        499         540
9       768        805         800
10      480        516        1190
11      720        749         670
12      540        562         670
13      300        313         750

Last edited: 06 December, 2020