|Location||QVME (Level E-19 Drivers onwards), SMSQ/E for Atari ST & TT (QVME cards only)|
Due to the multitude of monitors which are available for the Atari ST range, it is necessary to be able to alter the horizontal and vertical scan rates (default = 50Hz, the setting on standard QL monitors).
The first parameter specifies the frame rate (the horizontal scan rate), a setting of 70 (or more) will reduce flicker on most Atari monitors. If omitted or 0, the original value is unchanged.
The second parameter specifies the line rate (the vertical scan rate), although this is normally not required as it is equal to the frame rate multiplied by the total number of lines. If this parameter is omitted or zero, the original is recalculated by reference to the number of lines and the frame rate.
The total number of lines and line rate can be calculated by reference to the following program:
100 INPUT #0,'Enter y size of QL screen (DISP_SIZE) ';QLy 110 INPUT #0,'Enter horizontal frame rate (DISP_RATE) ';Frate 120 INPUT #0,'Enter vertical blank pixels setting (DISP_BLANK) ';Blanky 130 Total_y=QLy+Blanky 140 total_lines=Total_y*(Qly/QLy) 150 PRINT 'The total number of displayed lines will be ';total_lines 160 PRINT 'Line scan rate will be ';total_lines*Frate
If you use DISP_RATE to set the line scan rate, then using the total number of lines (and hence the blank lines) are recalculated, using the following routine:
100 INPUT #0,'Enter y size of QL screen (DISP_SIZE) ';QLy 110 INPUT #0,'Enter horizontal frame rate (DISP_RATE) ';Frate 120 INPUT #0,'Enter vertical line scan rate (DISP_RATE) ';Lrate 130 Total_y=INT(Lrate/Frate) 140 PRINT 'Blank Lines for DISP_BLANK will be ';Total_y-QLy
DISP_SIZE allows you to pass these parameters at the same time as amending the size of the displayed QL screen. DISP_BLANK sets the number of horizontal and vertical blank pixels on the edge of the display.
Both SMSQ/E and QVME include programs to allow you to try out the various settings for the DISP_… commands.