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Restrictions on Function Blocks Section 2-3
• Instructions manipulating record positions (PUSH, FIFO, LIFO, SETR,
and GETR)
• FAILURE POINT DETECTION Instruction (FPD)
• Move Timer/Counter PV to Register Instruction (MOVRW)
AT Setting Restrictions
(Unsupported Data Areas)
Addresses in the following areas cannot be used for AT settings.
• Index Registers (neither indirect nor direct addressing is supported) and
Data Registers
Note Input the address directly, not the AT setting.
• Indirect addressing of DM or EM Area addresses (Neither binary-mode
nor BCD-mode indirect addressing is supported.)
Direct Addressing of I/O
Memory in Instruction
Operands
• Addresses, not variables, can be directly input in Index Registers (both
indirect and direct addressing) and Data Registers.
The following values can be input in instruction operands:
Direct addressing: IR0 to IR15; Indirect addressing: ,IR0 to ,IR15; Con-
stant offset (example): +5,IR0; DR offset: DR0,IR0; Auto-increment:
,IR0++; Auto-decrement: --,IR0
• Direct addressing in instruction operands is not supported for any other
areas in I/O memory.
I/O Variable Restrictions
(Unsupported Data Areas)
Addresses in the following data areas cannot be used as parameters for input
and output variables.
• Index Registers (neither indirect nor direct addressing is supported) and
Data Registers
• Indirect addressing of DM or EM Area addresses (Neither binary-mode
nor BCD-mode indirect addressing is supported.)
Interlock Restrictions When a function block is called from an interlocked program section, the con-
tents of the function block definition will not be executed. The interlocked func-
tion block will behave just like an interlocked subroutine.
Differentiation
Instructions in Function
Block Definitions
An instance will not be executed while its EN input variable is OFF, so the fol-
lowing precautions are essential when using a Differentiation Instruction in a
function block definition. (Differentiation Instructions include DIFU, DIFD, and
any instruction with an @ or % prefix.)
• As long as the instance’s EN input variable is OFF, the execution condition
will retain its previous status (the last status when the EN input variable
was ON) and the Differentiation Instruction will not operate.
• When the instance’s EN input variable goes ON, the present execution
condition status will not be compared to the last cycle’s status. The
present execution condition will be compared to the last condition when
the EN input variable was ON, so the Differentiation Instruction will not
operate properly. (If the EN input variable remains ON, the Differentiation
Instruction will operate properly when the next rising edge or falling edge
occurs.)
FB
IL
P_Off
ILC
FB_BODY
Interlocked
Interlock will not
affect instructions in
the function block
definition.
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