Allen-Bradley MicroLogix 1200 Reference Manual page 200

14-18 File Instructions
Publication 1762-RM001C-EN-P
This instruction uses the following operands:
• LIFO - The LIFO 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 LIFO stack. The LFU
instruction unloads this value from the last location on the LIFO stack
and places it in the destination address. The address level of the
destination must match the LIFO stack. If LIFO is a word size file,
destination must be a word size file. If LIFO 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)
EU DN
Word 1 Length - maximum number of words or double 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 LIFO is empty.
• Length - The length operand contains the number of elements in the
LIFO stack. The length of the stack can range from 1 to 128 (word) or
1 to 64 (long word).
• Position - This is the next location in the LIFO stack where data will
be unloaded. 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.
Table 14.17 LFU Instruction Valid Addressing Modes and File Types
For definitions of the terms used in this table see Using the Instruction Descriptions on page4-2.
Data Files
Parameter
LIFO • • • •
Destination • • • • •
(2)
Control
Length
Position
(1) See Important note about indirect addressing.
(2) Control file only. Not valid for Timers and Counters.
You cannot use indirect addressing with: S, ST, MG, PD,
IMPORTANT
RTC, HSC, PTO, PWM, STI, EII, BHI, MMI, DAT, TPI, CS,
IOS, and DLS files.
12 11 10 9 8 7 6 5 4 3 2 1 0
(2) (3) not used
EM
Function Files
•
•
Address
Address
(1)
Level
Mode
• • • •
• • • •
• •
• •
• •