Page 278 - Programmable Logic Controllers, Fifth Edition - Mobile version

SQO Figure 12-12 shows an example of a ControlLogix
Sequencer Output EN time-driven sequencer output program. The program is
Array ? DN designed to execute a sequential process involving five
Mask ? steps which control several outputs. The outputs which
Dest ?
Control ? are on for each step are shown in the table. The operation
Length ? of the program can be summarized as follows:
Position ?
• The array parameter SQO_Data_Array contains the
Figure 12-11 ControlLogix Sequencer Output (SQO) desired output states for each step.
instruction. • The output states for each step are entered at the
starting location SQO_Data_Array[0].
the SLC 500 Sequencer Output instruction. The six pa- • In this application none of the outputs are energized
rameters entered into this instruction are: in step 0. When the SQO instruction executes, it
will be in step 0 on initial start-up.
• Array—An array tag of the type DINT is the first
entry you need to make. This is a word-level tag • When the SQO instruction advances to step 5, it
that defines the starting word of the sequencer data will return to step 1 and continue from there.
array. The desired output conditions for each step • The mask has a constant hexadecimal value of
are manually entered into the array in the tag editor. 0000_00FF which is the same as 0000 0000 0000
The ControlLogix processor puts the radix and the 0000 0000 0000 1111 1111 binary bits. Each bit
# sign in front of the value to indicate the radix of the corresponds to one output in the SQO instruction.
displayed number. For example, 16# (hexadecimal) • In this example the two hexadecimal Fs represent
or 2# (binary). 8 binary 1s in memory. A value of 1 in the mask
• Mask—The Mask works exactly like the mask in allows the output state from the step to be sent to
the MVM instruction. It can be a word level tag or the Dest.
a hexadecimal program constant. When the SQO • The DN (done) bit of the 5-second TON Step_
transfers 32-bits of data to an output word, there Timer is used to trigger the SQO instruction.
might be outputs associated with the word that do • Every time the timer ACC value reaches 5 seconds,
not need to be controlled by the SQO. By masking the timer DN bit changes state causing the SQO
these bits the SQO will not control them and they instruction to increment the Position number of the
could be used for other purposes in the program. Control tag and move to the next step.
• DEST—This is the word level data type DINT tag • Note that the timer DN bit also resets the ACC
where the data from the instruction will be sent. value of the timer to 0 and the timer starts timing
• Control—The tag of data type Control contains the to 5 seconds again.
control structure for the instruction. The Control tag
has several bits that can be used: enable (EN), done
(DN), error (ER), and so on. The control element 12.3 Sequencer Programs
also contains the Length of the sequencer (number of A sequencer program can be event-driven or time-driven.
steps) and the current Position (step in the sequence). An event-driven sequencer operates similarly to a me-
• Length—The length (LEN) parameter stores the chanical stepper switch that increments by one step for
value that defines the number of steps the sequencer each pulse applied to it. A time-driven sequencer oper-
should make. It also defines the number of words ates similarly to a mechanical drum switch that incre-
required in the sequencer array. Position 0 is the ments automatically after a preset time period.
start-up position. The first time the SQO instruc- A sequencer chart, such as the one shown in
tion is enabled it moves from position 0 to position Figure 12-13, is a table that lists the sequence of operation
1 when the instruction is toggled. The instruction of the outputs controlled by the sequencer instruction.
resets to position 1 at the end of the last step. The These tables use a matrix-style chart format. A matrix
array size must be at least one element larger than is a two-dimensional, rectangular array of quantities. A
the size of the length. time-driven sequencer chart usually indicates outputs on
• Position—The Position (POS) parameter stores the its horizontal axis and the time duration on its vertical
current step of the sequencer. Steps are numbered axis. An event-driven sequencer indicates outputs on its
starting at zero. horizontal axis and the input, or event, on its vertical axis.

Sequencer and Shift Register Instructions Chapter 12 259

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