Delta Tau GEO BRICK LV Manuel D’Utilisation

The RETURN command will typically be the last line of an Open Servo algorithm.  Putting it earlier in the 
algorithm will not cause the command data to be used any sooner by the Turbo PMAC.  If the Open 
Servo program is used for a task other than servo-loop closure, there is no need to use the RETURN 
command.  In this case, when the Open Servo algorithm reaches the CLOSE statement that is required at 
the end of the program, it will write a 0 to this holding register automatically. 

Turbo PMAC will take the resulting value and add the contents of the torque compensation register 
(usually from the motor’s TCOMP torque compensation table) to it. If Turbo PMAC is not performing 
commutation for this motor (Ixx01 bit 0 = 0), it will take this sum and copy it to the register specified by 
Ixx02.  If you do not use the RETURN command in this case, Turbo PMAC will still copy the zero value 
that it has placed in the holding register that would have been used by the RETURN command into the 
register specified by Ixx02. 

If Turbo PMAC is performing commutation for this motor (Ixx01 bit 0 = 1), it will use the resulting sum 
as the “quadrature current” (torque) command input to the commutation algorithm.  In this case, Ixx02 
specifies the multiple output registers from the commutation algorithm. 

The Ixx29 and Ixx79 offset terms are added automatically by Turbo PMAC, just as if the built-in servo 
algorithms were used. 

The returned value must be an integer value in the range –8,388,608 to +8,388,607.  Most of the 
command output ranges associated with Turbo PMAC’s automatic servo loops are expressed as 16-bit 
values, with a range of –32,768 to +32,767.  The values associated with RETURN are therefore 256 times 
larger.  The actual command output device will not necessarily have this full 24-bit resolution (and 
probably will not).  In general, however, an n-bit output device uses the high “n” bits of the 24-bit 
returned value. 

Variable Value Assignments 
Mathematical operations in an Open Servo algorithm are performed with variable value assignment 
statements, just as in other PMAC programs.  The syntactical rules for these statements are the same as in 
other PMAC interpreted and compiled programs.  Any I, P, Q, M, L, or F-variable can be assigned a 
value, whether referenced directly or as part of any array. 

Logical Control 
Logical branching and looping control in Open Servo algorithms is performed with IF / [ELSE] / ENDIF 
branching constructs, and WHILE / ENDWHILE looping constructs, just as in other PMAC programs.  The 
syntactical rules for these statements are the same as in PMAC PLC programs; they do not support a few 
features possible in motion programs (such as an action on the same line as a condition), and they do 
support a few features not possible in motion programs (such as multiple-line conditions).  Refer to the 
Program Command section of the Software Reference manual for details (see IF, ELSE, ENDIF, 
WHILE, ENDWHILE, AND, OR). 

If WHILE / ENDWHILE loops are used in an Open Servo, it is the user’s responsibility to make sure that 
the algorithm never gets stuck in a loop so long that other tasks are compromised.  Turbo PMAC will not 
release automatically from a loop in an Open Servo for any other task of equal or lower priority.  Failure 
to release from a loop in a timely fashion can result in servo error (failure to complete one cycle’s servo-
interrupt tasks by the next servo interrupt), run-time error (failure to compute commanded move 
equations in time for that move to start, causing the motion program to abort), or watchdog timer error 
(failure to cycle through all required tasks in a timely fashion, causing the Turbo PMAC to shut down 
completely).