Rockwell Automation 1771-DE Absolute Encoder Module User Manual - Manual (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