Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 162)

Block Transfer
Chapter 14
14-7
The block length heading of the instruction accepts any value from 00-63,
whether or not the value is valid for a particular module. Enter 00 for the
default value and/or a block length of 64.
The block length is stored in binary in the byte corresponding to the
module’s address in the output image table.
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.
ATTENTION: 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.
File Address
The file address is the first word of the file to which (or from which) the
transfer is made. The file address is stored 100 words above the data
address of the instruction. When the file address is entered into the
instruction block, the industrial terminal computes and displays the ending
address based on the block length.
When reserving an area for a block transfer file, select an appropriate
address to ensure that block transfer data does not write over assigned
timer/counter accumulated and preset values. The file address cannot
exceed address 5777
08
.