Rockwell Automation 1771-DB BASIC MODULE - Manual (Page 160)

Chapter
Statements 11
11 -8
Use the DO-UNTIL statement to set up loop control within a module
program. All statements between the DO and the UNTIL rel expr are
executed until the relational expression following the UNTIL statement is
true. You can nest DO-UNTIL loops.
The control stack (C-stack) stores all information associated with loop
control. The C-stack is 157 bytes long. DO-UNTIL loops use 3 bytes of
the C-stack.
Do not improperly exit this loop or a C-stack error occurs. See CLEARS
(page 11 -3).
Important: Excessive nesting exceeds the limits of the C-stack, generating
an error, and causing the module to enter Command mode.
For more information see control stack, page 8 -1.
Syntax
DO-UNTIL rel expr
Example
Simple DO-UNTIL Nested DO-UNTIL
>1 REM EXAMPLE PROGRAM >1 REM EXAMPLE PROGRAM
>10 A=0 >10 DO
>20 DO >20 A=A+1
>30 A=A+1 >30 DO
>40 PRINT A >40 C=C+1
>50 UNTIL A=4 >50 PRINT A,C,A*C
>60 PRINT “DONE” >60 UNTIL C=3
>70 END >70 C=0
>RUN >80 UNTIL A=3
1 >90 END
2 >RUN
3 1 1 1
4 1 2 2
DONE 1 3 3
>READY 2 1 2
2 2 4
2 3 6
3 1 3
3 2 6
3 3 9
>READY
DO-UNTIL