Rockwell-automation 1771-DE Absolute Encoder Module User Manual Manuel d'utilisateur télécharger pdf (Page 29)

Module/Processor Communication

Chapter 4

4Ć5

Bit 7 is the loss-of-input-power bit. It is set when input power is

lost; it is reset when power is restored and bit 6 is reset.

Bit 6 is the write-data-valid bit. It is set at power-up and when the

processor changes from the program mode to the run mode; it is reset

when the module receives valid data in a block-transfer-write

operation.

Bit 5 is unused.

Bit 4 is the non-BCD preset flag. It is set when any preset is in

non-BCD format.

Bits 3 through 0 are a binary or hexadecimal code that indicates which

preset is not in BCD format. (Refer to Appendix D for the value of

these bits.) The module identifies each incorrect preset in the order

it finds them (one at a time). Once you correct a preset, the module

continues to identify any non-BCD preset.

Word 2 indicates the current absolute position of the encoder in BCD.

Presets are interpreted by the module as absolute numbers to be compared

to the absolute position of the encoder shaft; they are not interpreted as

degrees of shaft rotation.

Thus, if you have a 0 to 999-position encoder, you program presets for

output 3, for example, as:

Preset 3A = 200

Preset 3B = 402

There is no restriction on which mode of comparison you can use for

preset A or preset B.

In this example, we assume the use of a 0 to 359-position encoder when

referring to degrees of shaft rotation.

If you want to turn on output 0 between shaft positions 330 (preset A) and

005 (preset B), you set:

the “greater than” and “equal to” bits for preset A

the “less than” and “equal to” bits for preset B

the ZT bit

Programming Example

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Rockwell-automation 1771-DE Absolute Encoder Module User Manual Manuel d'utilisateur Page 29