416 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Chapter 9 Array (File)/Shift Instructions (BSL, BSR, FFL, FFU, LFL, LFU)
FIFO Unload (FFU)
The FFU instruction unloads the value from position 0 (first position) of the
FIFO and stores that value in the Destination. The remaining data in the FIFO
shifts down one position.
Operands:
Relay Ladder
If you use a user-defined structure as the data type for the FIFO or Destination
operand, use the same structure for both operands.
Operand Type Format Description
FIFO SINT
INT
DINT
REAL
string
structure
Array tag FIFO to modify
Specify the first element of the FIFO
Do not use CONTROL.POS in the subscript
Destination SINT
INT
DINT
REAL
string
structure
Tag Value that exits the FIFO
The Destination value converts to the data type of the Destination tag. A
smaller integer converts to a larger integer by sign-extension.
Control CONTROL Tag Control structure for the operation
Typically use the same CONTROL as the
associated FFL
Length DINT Immediate Maximum number of elements the FIFO can
hold at one time
Position DINT Immediate Next location in the FIFO where the
instruction unloads data
Initial value is typically 0
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