Chapter 24
Sequencer Instructions
24–4
Status Bits of the Control Element
EN (bit 15) – The enable bit is set by a false-to-true rung transition and
indicates the SQO or SQC instruction is enabled. It follows the rung
condition.
DN (bit 13) – The done bit is set by the SQO or SQC instruction after it has
operated on the last word in the sequencer file. It is reset on the next
false-to-true rung transition after the rung goes false.
ER (bit 11) – The error 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.
FD (bit 08) – SQC only. The found bit indicates that a match has been found
between a compare of a word or file of input data, through a mask, to a word
or file of reference data for equality. When the status of all non-masked bits
in an input word match those of the corresponding reference word, the found
bit is set. The found bit is set when a match exists, otherwise it is cleared.
This bit is assessed each time the SQC instruction is evaluated while the rung
is true.
•
Length (word 1) – This is the number of words of the sequencer file
starting at position 1. Position 0 is the startup position. The instruction
resets (wraps) to position 1 at each cycle completion.
The address assigned for a sequencer file is step zero. Sequencer
instructions use 1 words of data table for each file referenced in
the instruction. This applies to the source, mask, and/or destination if
addressed as files.
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
from which the instruction moves data in a SQO instruction or to which
the instruction compares data in an SQC instruction.
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.
Application note: You may use the reset (RES) instruction to reset a
sequencer. All control bits (except FD) will be reset to zero. The Position
will also be set to zero. The RES instruction should be addressed to the
control register (R data file) you are using.
Operation - Sequencer Output
This output instruction steps through the sequencer file whose bits have been
set to control various output devices.
