Commodore Plus 4 - Page 352

340 Using Peripheral Devices
Example: This example should be run only on a formatted disk containing no information
you want to preserve. It allocates the desired block. Unless the block you specify
was already allocated, a DIRECTORY performed prior to running the program
shows one more free block than one performed after running the program.
10 0PEliri5,8,15,"I"
20 IFDSO0THEUPRI]SrTDS$:G0T080
30 OPEN1,8,2,"#"
40 IFDSO0THElSrPRINTDS$:G0T080
50 PRINT"WHICH TRACK, SECTOR" ;:INPUTT,S
60 PRINT#15/'B-A:'';0;T;S
70 IFDSOOTHENPRIITTDSI
80 CLOSE1:CLOSE15
Example:
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 Allocate the specified sector.
70 Check for error. If one is found, exit.
80 Close the files.
Block Free (B-F)
The block free command updates the BAM to show the designated sector as not
used. The BAM is actually written out to the disk when a direct-access channel is
closed, so it is a good idea to open and close a direct-access channel when freeing a
block, even if it is not needed for any other purpose. The syntax for a block free is
PRINT* filenumber,"B-'F:"; drive;track;seotor
where filenumber is the logical file number of the command 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.
This example should be run only on a formatted disk containing no information
you want to preserve. It frees the desired block. Unless the block you specify was