Rockwell-automation 1771-DB BASIC MODULE Manual de usuario descargar pdf (Pagina 175)

Chapter

Statements

11 -23

Use the ONERR statement to handle arithmetic errors, if they occur, during

program execution. The ONERR statement only traps arithmetic overflow

(value too large), arithmetic underflow (value too small), divide by zero,

and bad argument errors. All other errors are not trapped and cause the

BASIC module to enter the Command mode. If an arithmetic error occurs

after you execute the ONERR statement, the module interpreter passes

control to the line number (ln num) following the ONERR statement.

You handle the error condition in a manner suitable to your application.

The ONERR command does not trap bad data entered during an input

instruction. This yields a

TRY

AGAIN

message or EXTRA

IGNORED

message.

For expanded ONERR functionality, refer to CALL 38 on page 12 -36.

Note:

This statement did not work in the Series A module.

After you execute the ONERR statement, you can determine what type of

error occurred by examining external memory location 257 (101H).

The error codes are:

ERROR

CODE = 10–DIVIDE BY ZERO

ERROR

CODE = 13–DIVIDE SYNTAX ERROR

ERROR

CODE = 20–ARITH. OVERFLOW

ERROR

CODE = 30–ARITH.UNDERFLOW

ERROR

CODE = 40–BAD ARGUMENT

You can examine this value by using an XBY(257) special function

operator (page 9 -19). In addition, the line number can be determined by

this BASIC line 256*XBY(69FDH)+XBY(69FEH).

Syntax

ONERR

ln num

Example

1 REM EXAMPLE PROGRAM

10 ONERR 500

20 FOR I = 5 TO 0 STEP –1

30 PRINT 1/I

40 NEXT I

50 END

500 PRINT “ERROR CODE WAS ”,XBY(257)

510 PRINT ”AT LINE ” (256*XBY(69FDH)+XBY(69FEH)

)

510 END

READY

>RUN

.25

.33333333

ERROR CODE WAS 10

AT LINE 30

ONERR

A GOTO statement (page 11 -14) can replace

the END statement (page 11 -10) in this

example to provide a method of user

programmed error recovery.

1 2 ... 170 171 172 173 174 175 176 177 178 179 180 ... 393 394

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