Commodore Plus 4 - Page 343

The Disk Drive 331
180 Find out the name to add.
190 Trim off unusable characters.
200 Find out the number to add.
210 Trim off unusable characters.
220 Start with record number 1.
230 Position file pointer to beginning of record.
240 Save the error number in D. If no error, continue.
250 If a record not found error occurs, then here is the position to put a new
record. Otherwise, inform user, and quit.
260 Read the name on this record.
270 If it is a valid name, go on to next record. Otherwise, here is the position
to put a new record.
280 Position file pointer to beginning of record.
290 Read the error. If no error or a record not found error, ignore. Other
wise, inform user and quit.
300 Output the new name and number.
310 Close the files and quit.
User Files
The final file type that can be created with the OPEN command is a user file,
which is designated with a file type parameter of U. The user file type lets you
enter into the directory of the diskette a file with a user-defined structure. If it is
opened and written to in the normal manner, a user file has the structure of a
sequential file. Designing a custom file structure requires the use of the direct-
access commands detailed in the next section.
Diskette Maintenance A number of useful commands can be used to handle
diskettes. Most of these are available in two formats on the Plus/4. The Plus/4
supports BASIC 3.5 disk handling commands that may also be sent to the drive
through the command channel. The BASIC 3.5 commands detailed in Chapter 1
are reviewed. The equivalent command channel commands (which are especially
useful in machine language programming) are fully described here.
To use the command channel, it must first be opened with
OPEN" filenumber,device,lS