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Chapter 17
Sequencer Instructions
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Objectives
Describe the function of a sequencer.
Describe the operation of the SLC 500 sequencer output (SQO) instruction.
Explain the function of each SQO status bit.
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Objectives (cont’d.)
Explain the role of the control (R6) file.Explain the role of the bit file while
programming a sequencer instruction.Explain what a mask is and why it is
used.Determine the appropriate hexadecimal
mask for your application.
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Sequencer Instructions
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Sequencer Output Instruction (SQO)
SQO is an output instruction.Each false to true transition causes
the SQO instruction to increment to the next sequence step.
Sequencer steps are stored in a reference data file.
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SLC 500 PLC Sequencer Output
Instruction
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Bit File Containing Sequencer Step Data
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Sequencer Operation
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Sequencer Reference File #B3:0
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SQO Control File
Sequencer instructions do not have designated data files like timers or counters.
Use R6 control file.Control file will store sequencer
status bits, length, and position data.
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Three-Word Control Element for the SQO
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SQO and Associated Status Bits
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SQO and Hexadecimal Masking
Sequencers use hexadecimal masks similar to the MVM instruction to filter data from the sequencer reference file to the output destination.
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Only Bits 0 through 7 Will Be Allowed to Pass through the
Mask
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Only Bits Set to a 1 Will Allow Data to Pass
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Bit Pattern Translated to Hexadecimal
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Only Bits 8 through 11 Will Be Allowed to Pass through the
Mask
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Selected Single Mask Bits Set to a 1
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Bit Pattern Translated to Hexadecimal
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Binary Bit Pattern and Hex Correlations