10 'ROM instrument test program
20 screen,,0:out&hc6,5:out&hc7,3
30 i=0
40 printi;chr$(13);:out&h7e,32:out&h7f,i\256:out&h7e,8:out&h7f,iand255
41 forj=0to20:nextj:out&h7e,&h68:out&h7f,128
50 a$=input$(1):ifa$=chr$(32)thengoto100
60 ifa$=chr$(&h1c)theni=(i+1)and511:goto100
70 ifa$=chr$(&h1d)theni=i-1:ifi<0theni=511
100 out&h7e,&h68:out&h7f,0:forj=0to20:nextj:goto40