You also need to set the display window stopping position, which is the lower right-hand corner of the display window. If you select high resolution or interlaced mode, the stopping position does not change. Like the starting position, it is interpreted in low resolution, non-interlaced mode. The register DIWSTOP (for Display Window Stop) controls the display window stopping position. This register contains both the horizontal and vertical components of the display window stopping positions, known respectively as HSTOP and VSTOP. The instructions below show how to set HSTOP and VSTOP for the basic playfield, assuming a starting position of ($81,$2C). Note that the HSTOP value you write is the actual value minus 256 ($100). The HSTOP position is restricted to the right-hand side of the screen. The normal HSTOP value is ($1C1) but is written as ($C1). HSTOP is the same both for NTSC and for PAL. The VSTOP position is restricted to the lower half of the screen. This is accomplished in the hardware by forcing the MSB of the stop position to be the complement of the next MSB. This allows for a VSTOP position greater than 256 ($100) using only 8 bits. Normally, the VSTOP is set to ($F4) for NTSC, ($2C) for PAL. The normal NTSC DIWSTRT is ($2C81). The normal NTSC DIWSTOP is ($F4C1). The normal PAL DIWSTRT is ($2C81). The normal PAL DIWSTOP is ($2CC1). The following example sets DIWSTOP for a basic playfield to $F4 for the vertical position and $C1 for the horizontal position. LEA CUSTOM,a0 ; Get base address of custom hardware... MOVE.W #$F4C1,DIWSTOP(a0) ; Display window stop register... Table 3-9: DIWSTRT and DIWSTOP Summary Nominal Values Possible Values -------------- --------------- NTSC PAL MIN MAX ---- --- --- --- DIWSTRT : ---------- VSTART $2C $2C $00 $FF HSTART $81 $81 $00 $FF DIWSTOP: -------- VSTOP $F4 $2C (=$12C) $80 $7F (=$17F) HSTOP $C1 $C1 $00 (=$100) $FF (=$1FF) The minimum and maximum values for display windows have been extended in the enhanced version of the Amiga's custom chip set (ECS). See Appendix C, Enhanced Chip Set for more information about the display window registers .