Block Transfer
Chapter 10
1018
The programming of a bidirectional block transfer module depends on
whether the read and write instruction block lengths are equal or unequal.
Equal Block Lengths
When the block lengths are set equal or when the default block length is
specified by the programmer, the following considerations are applicable:
Read and write instructions could and should be enabled in the same
scan (separate but equal input conditions).
Module decides which operation will be performed first when both
instructions are enabled in the same scan.
Alternate operation will be performed in a subsequent scan.
Transferred data should not be operated upon until the Done bit is set.
Unequal Block Lengths
Consult the user’s manual for the block transfer module of interest for
programming guidelines when setting the block lengths to unequal values.
WARNING: When the block lengths of bidirectional block
transfer instructions are set to unequal values, the rung
containing the alternate instruction must not be enabled until
the done bit of the first transfer is set. If they are enabled in
the same scan, the number of words transferred may not be
the number intended, invalid data could be operated upon in
subsequent scans or analog output devices could be controlled
by invalid data. Unexpected and/or hazardous machine
operation could occur. Damage to equipment and/or personal
injury could result.
10.9.5
Programming
Considerations
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