Fifo Unload (Ffu); Relay Ladder - Allen-Bradley Logix5000 Reference Manual

Chapter 9 Array (File)/Shift Instructions (BSL, BSR, FFL, FFU, LFL, LFU)

FIFO Unload (FFU)

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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

Operand
FIFO
Destination
Control
Length
Position
If you use a user-defined structure as the data type for the FIFO or Destination
operand, use the same structure for both operands.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Type Format
SINT Array tag
INT
DINT
REAL
string
structure
SINT Tag
INT
DINT
REAL
string
structure
The Destination value converts to the data type of the Destination tag. A
smaller integer converts to a larger integer by sign-extension.
CONTROL Tag
DINT Immediate
DINT Immediate
Description
FIFO to modify
Specify the first element of the FIFO
Do not use CONTROL.POS in the subscript
Value that exits the FIFO
Control structure for the operation
Typically use the same CONTROL as the
associated FFL
Maximum number of elements the FIFO can
hold at one time
Next location in the FIFO where the
instruction unloads data
Initial value is typically 0