SQO — Sequencer Output

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Description

SQO (Sequencer Output) steps through a table of output patterns. Each time its rung goes from false to true it advances the control tag’s position by one, reads the array element at that position, and writes it to Dest through a mask; bits where the mask is 0 are left as they were in Dest. Use SQO for a drum-sequence machine: a wash cycle, a traffic light, an indexing table whose outputs change step by step. Do not use SQO where a step must wait on a condition before advancing; the rung itself must carry that condition, and a step that should hold outputs while waiting is simply a step the rung does not advance past.

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Operands

Operand	Type	Format	Valid Range	Required	Description
Control	CONTROL tag	Tag or Tag[n]	One SQO per control tag	Yes	Holds LEN, POS and the status bits.
File	INT or DINT array tag	Tag	At least Length + 1 elements	Yes	The table of patterns. Element 0 is the start position and is never output; steps are elements 1 to Length.
Mask	Whole number or tag	0x000F, 255, Tag	Any	Yes	Bits set to 1 in the mask are written to Dest; bits at 0 are left untouched.
Dest	Writable INT or DINT tag, member or element	Tag	Any	Yes	Where the step pattern is written.
Length	Whole number	4	1 to array size − 1	Yes	Number of steps.
Position	Whole number	0	0 to Length	No	Starting position at power-up; 0 is the usual choice.

The array must have one more element than Length, because positions run 1 to Length and element 0 is the parked position. The validator refuses a Length that would step past the end.

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Scan Behavior

Prescan

LEN is loaded from Length and POS from Position. Dest is not written.

Rung-condition-in is false

EN is cleared. Nothing advances; Dest keeps the last pattern written.

Rung-condition-in is true

On the scan the rung turns true, POS advances by one, wrapping from Length back to 1, and File[POS] is written to Dest through the mask. DN is set while POS equals Length and clear otherwise. Holding the rung true does nothing more.

Postscan

Nothing.

Condition	EN	DN	POS	Dest
Power-up	0	0	Position (usually 0)	holds
Rung false	0	holds	holds	holds
False → true	1	POS = LEN	+1, wrapping LEN → 1	(File[POS] & Mask) | (Dest & ~Mask)
Held true	1	holds	holds	holds
RES on the control	0	0	0	holds

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Member Bits

Bit	Mnemonic	Data type	Set by	Cleared by	Operation description
Enable	.EN	BOOL	The rung being true	The rung being false, or RES	Mirrors the rung condition.
Enable unload	.EU	BOOL	Never	RES	Reserved.
Done	.DN	BOOL	POS reaching LEN	The next advance (wrap to 1), or RES	The sequencer is on its last step. Use it to run an end-of-cycle action or to reset.
Empty	.EM	BOOL	Never	RES	Not used by SQO.
Error	.ER	BOOL	Never	RES	Reserved. A Length that overruns the array is refused at validation.
Unload	.UL	BOOL	Never	RES	Not used by SQO.
Inhibit	.IN	BOOL	Never	RES	Reserved.
Found	.FD	BOOL	Never	RES	Not used by SQO.
Length	.LEN	INT	Length at power-up	Never (RES preserves it)	Number of steps.
Position	.POS	INT	Each advance	RES (to 0)	The current step; 0 means parked before the first step.

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Example

Scenario: A four-station indexing table energises one output per station. The pattern table holds one bit per step, and the four low bits of Outputs drive the stations.

Tags:

• Seq_Step — Index complete, BOOL
• Steps — Pattern table, INT[5], loaded 0, 1, 2, 4, 8
• Outputs — Station outputs, INT
• SQO_Ctl — Control, CONTROL, Length 4

Rung 1:

—] [Seq_Step———[SQO SQO_Ctl  Steps  0x000F  Outputs  4]———

Scan 1 — Seq_Step = 0. Position 0, nothing has been output: Outputs reads 0 and DN is dark. The SQC and SQL rungs below are the examples from their own pages, parked. A File operand lists the array’s values, trimmed in the middle when it is long.

Scan 2 — Seq_Step = 1. Position advances to 1 and Steps[1] is written: Outputs reads 1, station 1 on.

Three more edges write 2, 4 and 8; on the fourth DN lights. The next edge wraps to position 1 and writes 1 again.

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Control Tag Errors and Troubleshooting

Error definitions

.ER cause	Condition that sets it	.POS / status value	Meaning
None	.ER is never set by LadderIDE	—	A File that is not an INT/DINT array, or a Length of array size or more, is refused when the project is validated.

Troubleshooting hints

Symptom: The first edge outputs step 1, not step 0. Likely cause: Position 0 is the parked start; the first advance goes to 1. Fix: Put the first real pattern in element 1. Element 0 is never output.

Symptom: Bits outside the sequence change unexpectedly. Likely cause: The mask covers bits other rungs also write, or the mask is wider than intended. Fix: Narrow the mask to exactly the bits the sequencer owns; other rungs may then drive the rest of Dest.

Symptom: The sequencer restarts at step 1 after a power cycle. Likely cause: POS is not retained; it is loaded from Position at power-up. Fix: That is the intended behaviour. A cycle that must resume needs its own step memory.

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See Also

• SQC — Sequencer Compare (check inputs against a table)
• SQL — Sequencer Load (teach the table from live values)
• RES — Reset (park at position 0)
• AND — Bitwise AND (the same masking on its own)
• Shift/Sequencer Instructions — Category index

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Notes

Timed steps. Drive the rung from a TON’s DN with the timer reset on each step; the sequencer advances once per timeout.

Dwell on a step. The outputs hold while the rung stays false, so a step that waits on a sensor is a rung condition, not a special step.

The block colours neutral. Watch the rung wire, the Position row and DN.