A2h XT$BAR prepare a bar graph display
Input A register - % of black on the left.
B register - % of grey on the right.
Output - none -

Sets up the udgs for drawing a bar graph as in the INFO application.

Also leaves characters for drawing the line in the runtime buffer (charcters for line in RTT_BF - RTT_BF+19, RTB_BL=20)

Calling this service with A+B>100 may cause unpredictable results.

This call is not available on CM/XP machines.

Example Draws a bar graph on the second line of the screen with 35% black and 17% grey.
        LDD     #(35*256+17)
        OS      XT$BAR
        LDX     #RTB_BL
        OS      UT$DISP
        DB      0Bh,0Ah    ;Home, Line feed
        ASCIZ   "%s"
Errors - none -