Allen-Bradley MicroLogix 1200 Reference Manual page 194

14-12 File Instructions
Publication 1762-RM001C-EN-P
This instruction uses the following operands:
• FIFO - The FIFO operand is the starting address of the stack.
• Destination - The destination operand is a word or long word address
that stores the value which exits from the FIFO stack. The FFU
instruction unloads this value from the first location on the FIFO stack
and places it in the destination address. The address level of the
destination must match the FIFO stack. If FIFO is a word size file,
destination must be a word size file. If FIFO is a long word size file,
destination must be a long word size file.
• Control - This is a control file address. The status bits, stack length,
and the position value are stored in this element. The control element
consists of 3 words:
15 14 13
Word 0 -- (1) (2)
EU DN
Word 1 Length - maximum number of words or long words in the stack.
Word 2 Position - the next available location where the instruction unloads data.
(1) EU - Enable Unload Bit is set on false-to-true transition of the rung and indicates the instruction is enabled.
(2) DN - Done Bit, when set, indicates that the stack is full.
(3) EM - Empty Bit, when set, indicates FIFO is empty.
• Length - The length operand contains the number of elements in the
FIFO stack. The length of the stack can range from 1 to 128 (word) or
1 to 64 (long word).
• Position - Position is a component of the control register. The position
can range from 0 to 127 (word) or 0 to 63 (long word). The position is
decremented after each unload. Data is unloaded at position zero.
12 11 10 9 8
(3) not used
EM
7 6 5 4 3 2 1 0