Commodore 1581 - Chapter 3: Basic 7.0 Commands; Error Checking

CHAPTER 3
BASIC 7.0 COMMANDS
This chapter describes the disk commands used with the Com
modore 128 computer (in C128 mode). This is BASIC 7.0, which
includes BASIC 2.0, BASIC 3.5, and BASIC 4.0 commands, all of which
can be used.
ERROR CHECKING
When the drive light (red light) flashes, you must use the follow
ing command to find out what the error is:
PRINT DS$
A message is displayed whether there is an error or not. If there
was an error, this command clears it from disk memory and turns off
the error light on the disk drive.
Once the message is on the screen, you can look it up in Appen
dix B to see what it means, and what to do about it.
For those of you who are writing programs, the following is a
small error-checking subroutine you can include in your programs:
59990 REM READ ERROR CHANNEL
60000 IF DS>1 THEN PRINT DS$:STOP
60010 RETURN
The subroutine reads the error channel and puts the results into
the reserved variables DS and DS$. They are updated automatically by
BASIC.
Two error numbers are harmless—0 means everything is OK, and
1 tells how many files were erased by a SCRATCH command (de
scribed later in this chapter). If the error status is anything else, line
60000 prints the error message and halts the program.
Because this is a subroutine, you access it with the BASIC GOSUB
command, either in immediate mode or from a program. The RETURN
statement in line 60010 will jump back to immediate mode or the next
statement in your program, whichever is appropriate.
SAVE
This command will save a program or file so you can reuse it. The
diskette must be formatted before you can save it to that diskette.
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