CPS — Synchronous Copy File

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Description

CPS (Synchronous Copy File) copies Length elements from one array to another every scan its rung is true, exactly as COP does. In Logix 5000 the difference is that CPS cannot be interrupted by an I/O update or a higher-priority task, so a block of values is guaranteed to be captured from one instant. A LadderIDE controller runs a single scan loop with nothing to interrupt it, so every copy is already synchronous and CPS generates the same code as COP. It exists so a program that documents its intent, or one brought across from Logix, reads the same way here. Use CPS where the reader should know the block must be consistent; use COP everywhere else.

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Operands

Operand	Type	Format	Valid Range	Required	Description
Source	Array tag, or an element of one	Tag, Tag[n]	Numeric or STRING array	Yes	Where copying starts.
Dest	Array tag, or an element of one	Tag, Tag[n]	Same kind as Source	Yes	Where copying lands.
Length	Whole number	4	1 up to what both arrays have room for	Yes	Elements copied.

The validation rules are COP’s.

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Scan Behavior

Prescan

Nothing.

Rung-condition-in is false

The instruction does nothing. Dest holds.

Rung-condition-in is true

Elements are copied in order, every scan the rung is true, within the scan.

Postscan

Nothing.

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Example

Scenario: Four live readings are captured together into a snapshot array for a log record, so the record cannot mix values from two different scans.

Tags:

• Snap — Take the snapshot, BOOL
• Live_Vals — Live readings, INT[4], reading 5, 6, 7, 8
• Snapshot — Captured readings, INT[4]

Rung 1:

—] [Snap———[CPS Live_Vals  Snapshot  4]———

Scan 1 — Snap = 0. Live_Vals reads 5, 6, 7, 8 and Snapshot reads 0, 0, 0, 0.

Scan 2 — Snap = 1. Snapshot reads 5, 6, 7, 8.

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See Also

• COP — Copy File (offsets, overlap, and the every-scan note)
• FLL — Fill File
• Move/Logical Instructions — Category index

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Notes

Why it is the same here. Inputs are read once at the top of the scan and outputs written once at the bottom; the ladder in between sees one consistent set of values whichever copy instruction it uses.

The block never colours. Watch the rung wire and the Dest value list.