Commodore VIC-20 User Manual page 288

274
The VIC 20 User Guide
79 A=T
89
B=S
Note: If there are no more available sectors on the diskette, the error
channel will return track 0 and sector O. These do not designate a real sector
and will cause an error if you try to write to that location. To make sure you
don't have this problem, recheck the error channel. If there are zeros in
variables T and S, then you need to check for sectors with lower numbers.
99 IF A=9 AND B=0 THEN PRINT "DISK FULL":GOTO 160
If you don't get this error, continue with your BLOCK-WRITE.
199 PRHn "TRACK"; A;" "; "SECTOR";
B
195 OPEN
2,8,4,"#"
119 INPUT
A$
If you input an X, the program will terminate data input.
129 IF AS • "X" THEN 150
If not, then put the data into your file
130 PRINT4t2, AS
and go back for more.
149 GOTO 119
Use the following statement to put the data into your selected sector:
159 PRINT*15, "B-W: "4; 9; A; B
Note: The format of the BLOCK-WRITE instruction is the same as
that of the BLOCK-READ instruction.
Once more, you must close your files and end the program.
169 CLOSE 2: CLOSE 15
BUFFER·POINTER
As you have seen, the data buffer stores information that is read in
from the diskette. The buffer pointer keeps track of which byte is being read
and advances by one each time a byte is read.