Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 330)

Chapter 24
Sequencer Instructions
24–8
Status Bits
•
EN (bit 15) – The enable bit. This bit is set on a false-to-true transition
of the SQL rung and reset on a true-to-false transition.
•
DN (bit 13) – The done bit. This bit is set after the instruction has
operated on the last word in the sequencer load file. It is reset on the next
false-to-true rung transition after the rung goes false.
•
ER (bit 11) – The error bit. This bit is set when the processor detects a
negative position value, or a negative or zero length value. This results in
a major error if not cleared before the END or TND instruction is
executed. Use an OTU with address S:5/2 to avoid a CPU fault.
•
Length (word 1) – This is the number of steps of the sequencer load file
(and also of the source if the source is a file address), starting at position
1. Position 0 is the startup position. The instruction automatically resets
(wraps) to position 1 at each cycle completion.
The position address assigned for a sequencer file is step zero. Sequencer
instructions use length plus 1 word of data for each file referenced in the
instruction. This applies to the source if addressed as a file.
A length value that points past the end of the programmed file causes a
runtime major error to occur. If you alter a length value with your ladder
program, make certain that the altered value is valid.
•
Position (word 2) – This is the word location or step in the sequencer file
to which data is moved.
A position value that points past the end of the programmed file causes a
runtime major error to occur. If you alter a position value with your
ladder program, make certain that the altered value is valid.