OR — Bitwise OR

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Description

OR (Bitwise OR) writes to Dest a word whose every bit is 1 where the same bit is 1 in Source A or in Source B or in both. It is an output instruction with no state and no status bits. Use OR to set bits in a word without disturbing the others, to merge two command words into one output word, or to build a bit pattern from parts. Do not use OR to combine rung conditions; a parallel branch does that. OR works on whole numbers.

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Operands

Operand	Type	Format	Valid Range	Required	Description
Source A	A whole-number tag, member, element or bit, or a literal	Tag, Tag.Member, Tag[n], Tag.bit, a number	Any resolvable reference	Yes	The first word.
Source B	Same as Source A	Same	Any resolvable reference	Yes	The second word, often the bits to set.
Dest	A writable whole-number tag, member or element	Tag, Tag.Member, Tag[n]	SINT, INT or DINT; not a literal, not an input pin	Yes	Where the result is written.

A REAL operand is truncated to a whole number first. Dest may be one of the sources, which is how bits are set in place.

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Scan Behavior

Prescan

Nothing. Dest keeps its power-up value.

Rung-condition-in is false

The instruction does nothing. Dest holds its last value.

Rung-condition-in is true

Both sources are read, ORed bit by bit, and the result is written to Dest every scan the rung is true.

Postscan

Nothing.

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Example

Scenario: An output module is driven by one word. The sequence writes its command bits and a maintenance screen can force extra outputs on. The two words are merged into the word the module reads.

Tags:

• Set_Bits — Merge the words, BOOL
• Cmd_Word — Sequence command bits, INT
• Force_Word — Maintenance force bits, INT
• Out_Word — Word sent to the module, INT

Rung 1:

—] [Set_Bits———[OR Cmd_Word  Force_Word  Out_Word]———

Scan 1 — Set_Bits = 0. Cmd_Word reads 5 and Force_Word reads 8. The rung is false: Out_Word holds 0.

Scan 2 — Set_Bits = 1. Out_Word reads 13.

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Binary Result

OR — Cmd_Word OR Force_Word, INT (16 bits)

                 15 14 13 12  11 10  9  8   7  6  5  4   3  2  1  0
Cmd_Word     5    0  0  0  0   0  0  0  0   0  0  0  0   0  1  0  1
Force_Word   8    0  0  0  0   0  0  0  0   0  0  0  0   1  0  0  0
Out_Word    13    0  0  0  0   0  0  0  0   0  0  0  0   1  1  0  1
                                                         ^  ^     ^
                                              set where either is 1

A bit set in both sources is still one bit in the result; OR never carries.

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See Also

• AND — Bitwise AND (keep or clear bits)
• XOR — Bitwise XOR (toggle bits)
• NOT — Bitwise NOT
• OTL — Output Latch (set a single bit and keep it)
• Move/Logical Instructions — Category index

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Notes

Set in place. OR Word 0x0004 Word sets bit 2 and leaves the rest. Gating is unnecessary; setting an already-set bit changes nothing.

Not addition. 5 OR 8 is 13 and so is 5 + 8, but 5 OR 4 is 5 while 5 + 4 is 9. Use ADD for arithmetic.

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