Delta Tau GEO BRICK LV User Manual
Turbo PMAC User Manual
Turbo PMAC Computational Features
249
Variable Value Assignment Statement
This type of statement calculates and assigns a value to a variable. When a value assignment statement is
sent to Turbo PMAC, if a program buffer is open, the statement is added to the buffer. If not, it is
executed immediately. The standard assignment syntax is:
sent to Turbo PMAC, if a program buffer is open, the statement is added to the buffer. If not, it is
executed immediately. The standard assignment syntax is:
{variable name}={expression}
where {variable name} specifies which variable is to be used, and {expression} represents the
value to be assigned to the variable.
value to be assigned to the variable.
I-Variable Default Value Assignment
A statement with the syntax:
{I-variable}=*
will assign to the specified I-variable the manufacturer’s default value for that variable (not the user’s last
saved value).
saved value).
Synchronous M-Variable Value Assignment
In a motion program, when Turbo PMAC is blending or splining moves together, it must be calculating in
the program ahead of the actual point of movement. This is necessary in order to be able to blend moves
together at all, and also to be able to do reasonable velocity and acceleration limiting. Depending on the
mode of movement, calculations while blending may occur one, two, or three moves ahead of the actual
movement.
the program ahead of the actual point of movement. This is necessary in order to be able to blend moves
together at all, and also to be able to do reasonable velocity and acceleration limiting. Depending on the
mode of movement, calculations while blending may occur one, two, or three moves ahead of the actual
movement.
Why Needed
When assigning values to variables is part of the calculation, the variables will get their new values ahead
of their place in the program when looking at actual move execution. Generally, for P and Q-variables,
this is not a problem, because they exist only to aid further motion calculations. However, for M-
variables, particularly outputs, this can be a problem, because with a normal variable value assignment
statement, the action will take place sooner than is expected, looking at the statement’s place in the
program.
For example, in the program segment
of their place in the program when looking at actual move execution. Generally, for P and Q-variables,
this is not a problem, because they exist only to aid further motion calculations. However, for M-
variables, particularly outputs, this can be a problem, because with a normal variable value assignment
statement, the action will take place sooner than is expected, looking at the statement’s place in the
program.
For example, in the program segment
X10
; Move X-axis to 10
M1=1
; Turn on Output 1
X20
; Move X-axis to 20
it might be expected that Output 1 would be turned on at the time the X-axis reached position 10. But
since Turbo PMAC is calculating ahead, at the beginning of the move to X10, it will have already
calculated through the program to the next move, working through all program statements in between,
including M1=1, which turns on the output. Therefore, using this technique, the output will be turned on
sooner than desired.
since Turbo PMAC is calculating ahead, at the beginning of the move to X10, it will have already
calculated through the program to the next move, working through all program statements in between,
including M1=1, which turns on the output. Therefore, using this technique, the output will be turned on
sooner than desired.
How They Work
Synchronous M-variable assignment statements were implemented as a solution to this problem. When
one of these statements is encountered in the program, it is not executed immediately; rather, the action is
put on a stack for execution at the start of the actual execution of the next move in the program. This
makes the output action properly synchronous with the motion action.
In the modified program segment
one of these statements is encountered in the program, it is not executed immediately; rather, the action is
put on a stack for execution at the start of the actual execution of the next move in the program. This
makes the output action properly synchronous with the motion action.
In the modified program segment
X10
; Move X-axis to 10
M1==1
; Turn on Output 1 synchronously
X20
; Move X-axis to 20
the statement M1==1 (the double-equals indicates synchronous assignment) is encountered at the
beginning of the move to X10, but the action is not actually performed until the start of blending into the
next move (X20).
beginning of the move to X10, but the action is not actually performed until the start of blending into the
next move (X20).