Commodore Plus 4 - Page 355

The Disk Drive 343
fUenximber"B-l£:"channel;drive;track;sector
where filenumber is the logical file number of the command channel, channel is
the channel number of the direct-access channel, and drive is the drive number.
The track can be any track on the diskette (1 to 35) and the sector any sector of
that track.
Example: This example should be run only on a formatted disk containing no information
you want to preserve. The program writes a short machine-language subroutine
onto sector 0 of track 1, then block executes that sector. The subroutine examines
the 1541's memory to determine which of its internal buffers (0 through 7) is being
used, stores this information in the buffer for the BASIC program's retrieval, and
returns.
10 OPEN15,8,15,"I"
20 IFDSO0THENPRINTDS$:GOTO160
30 OPEN1,8,2,"#"
40 IFDSO0THENPRINTDS$:QOTO160
50 PRINT#15,lfB-P:";2;0
60 FORI=0TO6:READN
70 PRINT#1,CHR$(N);
80 NEXT
90 PRINT#15,"U2:"2;0;1;0
100 IFDSO0THENPRINTDS$:GOTO160
110 PRINTS15,"B-E:";2;0;1;0
120 IFDSO0THENPRINTDS$:GOTO160
130 PRINTS15,"B-P:";2,-7
140 GET#1,A$
150 PRINT"USING BUFFER: ";ASC(A$)
160 CLOSE1:CLOSE15
170 DATA 160,7,165,249,145,48,96
Line-by-Line Explanation
10 Open the command channel and initialize the disk.
20 Check for error. If an error is present, exit.
30 Open a direct access channel.
40 Check for error. If an error is present, exit.
50 Set buffer pointer to byte 0.
60 I counts the bytes in the machine-language routine.
70 Put a byte in the buffer.
80 Go on to the next byte.
90 Write buffer out to track 1, sector 0.