1 REM =====================================================
2 REM  DISK-ACCESS.BAS — C64 1541 Disk I/O Examples
3 REM  Demonstrates: sequential files, relative files,
4 REM  error channel, directory reading
5 REM =====================================================

100 REM =====================
101 REM SECTION 1: ERROR CHANNEL SUBROUTINE
102 REM =====================
103 REM Call GOSUB 9000 after any disk operation
104 REM Sets EN=error number, EM$=message, ET=track, ES=sector
105 GOTO 200

9000 REM --- READ ERROR CHANNEL ---
9010 OPEN 15,8,15
9020 INPUT#15, EN, EM$, ET, ES
9030 CLOSE 15
9040 IF EN > 1 THEN PRINT "DISK ERROR" EN EM$ "T"ET "S"ES
9050 RETURN

200 REM =====================
201 REM SECTION 2: WRITE SEQUENTIAL FILE
202 REM =====================
210 PRINT "WRITING SEQUENTIAL FILE..."
220 OPEN 1, 8, 2, "MYDATA,S,W"
230 GOSUB 9000 : IF EN > 1 THEN GOTO 299

240 PRINT#1, "RECORD 1"
250 PRINT#1, "RECORD 2"
260 PRINT#1, 12345
270 PRINT#1, "LAST RECORD"
280 CLOSE 1
290 GOSUB 9000
299 PRINT "WRITE DONE."

300 REM =====================
301 REM SECTION 3: READ SEQUENTIAL FILE
302 REM =====================
310 PRINT "READING SEQUENTIAL FILE..."
320 OPEN 1, 8, 2, "MYDATA,S,R"
330 GOSUB 9000 : IF EN > 1 THEN GOTO 399

340 IF ST <> 0 THEN GOTO 380    : REM check status
350 INPUT#1, LINE$
360 PRINT "READ: "; LINE$
370 GOTO 340
380 CLOSE 1
390 GOSUB 9000
399 PRINT "READ DONE."

400 REM =====================
401 REM SECTION 4: READ DIRECTORY
402 REM =====================
410 PRINT "DIRECTORY:"
420 LOAD "$",8
430 REM (After LOAD, program is gone! Use OPEN method instead:)
440 REM Alternative: open $ and read it
450 OPEN 1, 8, 0, "$"
460 GET#1, A$, B$  : REM skip first two bytes (load address)
470 LOOP$=""
480 GET#1, A$ : IF ST<>0 THEN GOTO 520
490 IF A$ = CHR$(0) THEN GOTO 480  : REM skip nulls
500 IF ASC(A$+CHR$(0)) = 13 THEN PRINT LOOP$ : LOOP$="" : GOTO 480
510 LOOP$ = LOOP$ + A$ : GOTO 480
520 IF LOOP$ <> "" THEN PRINT LOOP$
530 CLOSE 1

600 REM =====================
601 REM SECTION 5: SEND DOS COMMANDS
602 REM =====================
610 REM Scratch a file
620 PRINT "SCRATCHING OLD BACKUP..."
630 OPEN 15,8,15,"S0:BACKUP"
640 CLOSE 15
650 GOSUB 9000

660 REM Rename a file
670 PRINT "RENAMING FILE..."
680 OPEN 15,8,15,"R0:NEWNAME=MYDATA"
690 CLOSE 15
700 GOSUB 9000

710 REM Validate disk
720 PRINT "VALIDATING DISK..."
730 OPEN 15,8,15,"V0:"
740 CLOSE 15
750 GOSUB 9000

800 REM =====================
801 REM SECTION 6: LOAD ML PROGRAM
802 REM =====================
810 REM Load ML at its original address (SA=1)
820 LOAD "MLPROG",8,1
830 REM (after LOAD, program continues or use SYS)
840 END

900 REM =====================
901 REM SUBROUTINE: WAIT FOR KEY
902 REM =====================
910 PRINT "PRESS ANY KEY..."
920 GET K$ : IF K$="" THEN GOTO 920
930 RETURN