Commodore 1581 - Error Checking

ERROR CHECKING
In Basic 2.0, when the red drive light flashes, you must write a
small program to find out what the error is. This causes you to lose any
program variables already in memory. The following is the error
check program:
10OPEN15,8,15
20 INPUT#15,EN,EM$,ET,ES
30 PRINT EN, EM$,ET,ES
40 CLOSE15
This little program reads the error channel into four BASIC
variables (described below), and prints the results on the screen. A
message is displayed whether there is an error or not, but if there was
an error, the program clears it from disk memory and stops the error
light from blinking.
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:
59980 REM READ ERROR CHANNEL
59990 INPUT#15,EN,EM$,ET,ES
60000 IF EN>1 THEN PRINT EN,EM$,ET,ES:STOP
60010 RETURN
This assumes file 15 was opened earlier in the program, and that
it will be closed at the end of the program.
The subroutine reads the error channel and puts the results into
the named variables—EN (Error Number), EM$ (Error Message), ET
(Error Track), and ES (Error Sector). Of the four, only EM$ has to be a
string. You could choose other variable names, although these have
become traditional for this use.
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.
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