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Turbo PMAC User Manual
Writing and Executing PLC Programs
377
For variables referencing fixed locations in Turbo PMAC’s memory and I/O space, the L-variables will
simply replace M-variables, and the L-variable definition will be made exactly like the M-variable
definitions. It is completely acceptable to retain the M-variable definition as well. You will probably
want to retain the M-variable definitions for debugging purposes, because Turbo PMAC will not accept a
query command for the value or definition of an L-variable. Often, you will use identical L-variable and
M-variable definitions.
simply replace M-variables, and the L-variable definition will be made exactly like the M-variable
definitions. It is completely acceptable to retain the M-variable definition as well. You will probably
want to retain the M-variable definitions for debugging purposes, because Turbo PMAC will not accept a
query command for the value or definition of an L-variable. Often, you will use identical L-variable and
M-variable definitions.
For example, Machine Output 1 and Machine Input 1 on the JOPTO port typically are referenced by the
following definitions in uncompiled programs:
following definitions in uncompiled programs:
M1->Y:$078F02,8
; Machine Output 1
M11->Y:$078F02,0
; Machine Input 1
For the compiled PLC programs, you could create equivalent M-variable definitions:
L1->Y:$078F02,8
; Machine Output 1
L11->Y:$078F02,0
; Machine Input 1
A small routine in a compiled PLC to make Machine Output 1 follow Machine Input 1 would be:
IF
(L11=1)
L1=1
ELSE
L1=0
ENDIF
You may access a register in one program statement with an L-variable, and then access the same register,
even the same part of the register, in another program statement with an integer M-variable or I-variable.
Mixing L-variable access and P- or Q-variable access to a P- or Q-variable register will yield nonsensical
results, because the P- and Q-variable access always treats the register as a floating-point number.
even the same part of the register, in another program statement with an integer M-variable or I-variable.
Mixing L-variable access and P- or Q-variable access to a P- or Q-variable register will yield nonsensical
results, because the P- and Q-variable access always treats the register as a floating-point number.
F-Variables: Long Floating-Point Pointers
F-variables are pointers to long (48-bit) registers. If the F-variable definition is an L format (e.g. F1-
>L:$10F0), the register is accessed as a 48-bit floating-point register. If the F-variable definition is a D
format variable (e.g. F2->D:$88), the register is accessed as a 48-bit signed integer, but conversion to
or from Turbo PMAC’s 48-bit floating-point format is automatically performed, so it can be used in
floating-point mathematics.
F-variables are pointers to long (48-bit) registers. If the F-variable definition is an L format (e.g. F1-
>L:$10F0), the register is accessed as a 48-bit floating-point register. If the F-variable definition is a D
format variable (e.g. F2->D:$88), the register is accessed as a 48-bit signed integer, but conversion to
or from Turbo PMAC’s 48-bit floating-point format is automatically performed, so it can be used in
floating-point mathematics.
Note:
The use of F-variables requires the PRO series of PMAC Executive program
(PEWIN32PRO) and Turbo PMAC firmware revision 1.938 or newer.
(PEWIN32PRO) and Turbo PMAC firmware revision 1.938 or newer.
Turbo PMAC itself cannot recognize L-variables or F-variables; these variables have meaning only to the
compiler on the host computer. Turbo PMAC will reject any uncompiled command containing an L-
variable that is sent to it.
compiler on the host computer. Turbo PMAC will reject any uncompiled command containing an L-
variable that is sent to it.
Note:
Do not confuse L-variables, which are short-word compiler pointers, with L-format
F-variables and M-variables, which are long-word variables.
F-variables and M-variables, which are long-word variables.
Comparison to Run-Time Linked Pointers
By contrast, when using Turbo PMAC’s M-variable pointers, the register assignment is made when the
line is executed, each time it is executed. This assignment requires about 600 nanoseconds additional
computation time (on a 100 MHz CPU) each time the variable is accessed. However, this does permit the
M-variable definition to be changed during execution, enabling techniques such as indirect addressing.
By contrast, when using Turbo PMAC’s M-variable pointers, the register assignment is made when the
line is executed, each time it is executed. This assignment requires about 600 nanoseconds additional
computation time (on a 100 MHz CPU) each time the variable is accessed. However, this does permit the
M-variable definition to be changed during execution, enabling techniques such as indirect addressing.