Rockwell Automation 1771-DB Basic Module User Manual - Series A - Manual (Page 160)

Error Messages and Anomalies
Chapter 9
9–8
2. When using the variable I before an ELSE statement, put a space between
the I and the ELSE statement. If you do not, the program assumes that
the IE portion of IELSE is the special function operator IE.
This error may or may not yield a BAD SYNTAX — IN LINE XXX
error message, depending on the particular program in which it is
used.
Examples:
Wrong
u20 IF I u10 THEN PRINT IELSE 100
uLIST
20
IF I
u10 THEN
PRINT I ELSE 100
Right
u20
IF I
u10 THEN
PRINT I ELSE 100
uLIST
20
IF I
u10 THEN
PRINT I ELSE 100
3. Do not place a space character inside the ASC() operator. A statement
like PRINT ASC() yields a BAD SYNTAX ERROR. You can put spaces
in strings, however, allowing the following statement to work properly:
LET $(1)
u“HELLO, HOW ARE YOU”
ASC() yields an error because the module eliminates all spaces when
a line is processed. ASC() is stored as ASC() and the module
interprets this as an error.
4. Do not use the following one letter variables: B, F, R. Unpredictable
operation could result.
5. Do not use the following two letter variables: CR, DO, lE, IF, IP, ON, PI,
SP, TO, UI and UO.
6. When using an INPUT statement to enter data you must be sure to enter
valid data. If you enter invalid data you see the prompt “TRY AGAIN”.
This disrupts the screen layout.
7. SQR(M–M2) gives a bad argument if M=O.
8. ONTIME does not interrupt CALL routines, INPUT statements or
PRINT# statements waiting for handshaking (XON, CTS, DCD) to
become true. ONTIME is a polling mechanism which is checked after
each line of BASIC is completed. End of line is either a (CR) or (:).
9.4
Anomalies (continued)