100 OPEN2,2,3,CHR$(5)+CHR$(0)
110 PRINT"WAITING..."
120 GOSUB 400:IF A$<>"S" THEN 120
130 GOSUB 400:IF A$="S" THEN 130
140 C=A:I=A:GOSUB 400:I=I+A*256
150 GOSUB 400:E=A:GOSUB 400:E=E+A*256
160 GOSUB 400:PRINT"*";:POKEI,A:I=I+1:IF I<>E THEN 160
170 GOSUB 400:IF C<>0 THEN PRINT:PRINT"?CHK ERROR":CLOSE2:END
180 PRINT:PRINT"CHK OK":CLOSE2:END
400 GET#2,A$:IF ST=8 THEN 400
410 IF A$="" THEN A$=CHR$(0)
420 A=ASC(A$):C=(C+A)AND255:RETURN