Commodore Plus 4 - Page 353

The Disk Drive 341
not allocated, a DIRECTORY performed prior to running the program shows
one less free block than one performed after running the program.
10 0PEN15,8,15,"I"
20 IPDS<>0THElTPRI]SrTDS$:G0T080
30 OPE1T1,8,2,"#"
40 IPDSOOTHElTPRINTDSiiGOTOSO
50 PRINT//WHICHTI^CK,SECTOR//;:I]SrPUTT,S
60 PRI]STT#1S//B-F://;O;T;S
70 IPDSOOTHENPRIHTTDSI
80 CL0SEl:CL0SE15
Line-by-Line Explanation
10 Open the command channel and initialize the disk.
20 Check for error. If one is found, exit.
30 Open the direct access channel.
40 Check for error. If one is found, exit.
50 Ask which track and sector to use.
60 Free the specified sector.
70 Check for error. If one is found, exit.
80 Close the files.
Buffer Pointer (B-P)
The buffer pointer command designates the position in the 1541 buffer to access.
This command can be used before reading from the buffer to start GETting bytes
from a position other than the beginning of the buffer. B-P can be used before
writing to the buffer to start writing at a position other than the beginning. The
syntax for the buffer pointer command is
PRINT* filenumber,"B-P:"; channel;position
where filenumber is the logical file number of the command channel and channel
is the channel number of the direct-access channel. The position can be any byte
in the buffer (0 to 255).
Example: This example reads the first sector of the directory, moves the buffer pointer to
the first byte of the first file name in the directory, and prints out the first file
name.