ORG&H7000
START A
A:PST IA,13    ;Keyboard:all key output
PRE IZ,&H68C9  ;SCTOP (LCD-Offset)
LD$28,0        ;set=0 (first bitmap)
ST$28,(IZ+0)
CAL&H22C       ;DOTDI bitplane 0
LDW$28,812     ;2/3 of the Time 
R1:SBW$28,$30
JR NZ,R1       ;Delay Loop T1
GRE KY,$0      ;Check Keyboard
OR $0,$0      
RTN NZ         ;Exit on key press
PRE IZ,&H68C9  ;SCTOP (LCD-Offset)
LD$28,128      ;set=128 (second bitmap)
ST$28,(IZ+0)
CAL&H22C       ;DOTDI bitplane 1
LDW$28,367     ;1/3 of the Time
R2:SBW$28,$30
JR NZ,R2       ;Delay Loop T2
GRE KY,$0      ;Any Key pressed?
OR $0,$0
JR A           ;loop from beginning