Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 318)

Instructions
Chapter 23
Bit Shift, FIFO, and LIFO
23–6
Entering Parameters
Enter the following parameters when programming these instructions:
•
Source – This word address stores the value to be entered next into the
FIFO stack. The FFL instruction places this value into the next available
element in the FIFO stack. SOURCE can be a word address or a program
constant (–32768 to 32767). For I/O addresses, the HHT requires you to
specify the slot and word number, for example I:3.0.
•
Destination (Dest) – This word address stores the value that exits from
the FIFO stack. The FFU instruction unloads this value from the stack
and places it in this word address. For I/O addresses, the HHT requires
you to specify the slot and word number, for example O:3.0.
•
FIFO – This is the address of the stack. It must be an indexed word
address in the input, output, status, bit, or integer file. The same address
is programmed for the FFL and FFU instructions.
•
Control – This is a control file (R data file) address. The status bits, the
stack length, and the position value are stored in this element. The same
address is programmed for the FFL and FFU instructions. Do not use the
control file address for any other instruction.
The 3-word control element:
EN EU DN EM
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Length
Position
Status Bits
•
EN (bit 15) – FFL instruction enable bit. The bit is set on a false-to-true
transition of the FFL rung and is reset on a true-to-false transition.
•
EU (bit 14) – FFU instruction enable bit. The bit is set on a false-to-true
transition of the FFU rung and is reset on a true-to-false transition.
•
DN (bit 13) – Done bit. It is set by the FFL instruction to indicate the
stack is full. This inhibits loading the stack.
•
EM (bit 12) – Empty bit. It is set by the FFU instruction to indicate the
stack is empty.
•
Length (word 1) – This is the length of the stack, the maximum number
of elements in the stack, up to a maximum of 128 words. The same
number is programmed for the FFL and FFU instructions.
•
Position (word 2) – The next available location where the instruction
loads data into the stack. This value changes after each load or unload
operation. The same number is used for the FFL and FFU instructions.