Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 96)

Advanced Instruction Set
Chapter 6
6Ć39
programmed by assigning the get and put instructions to the address
immediately following the last block transfer data address. The value of the get
instruction is reset to 000 when programmed.
Defining the Block Transfer Data Address Area
When the block transfer instructions are used, the first word and consecutive
words of the timer/counter accumulated area of the data table must be reserved
for block transfer data addresses.
Block transfer data addresses should be separated from the addresses of timer
and counter instructions by inserting a boundary. When the processor sees this
boundary word, it will not search further for block transfer data. In addition,
the processor is prevented from finding other BCD values that could, by chance,
be in the same configuration as the rack, group and slot numbers found in block
transfer data addresses.
Block Length
The block length is the number of words that the module will transfer. it
depends on the type of module and the number of channels connected to it. The
number of words requested by the instruction (block length value) must be a
valid number for the module: i.e. from 1 up to the maximum for the module.
The block length can also be set at the default value of the module. This is
useful when programming bidirectional block transfers. See chapter 11.
The block length heading of the instruction will accept any value from 00 to 63
whether or not the number is valid for a particular module. A value of 00 is
entered for the default value and/or for 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.
File Address
The file address is the first word of the file to which (or from which) the
transfer will be made. The file address is stored 1008 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, an appropriate address must be
selected to ensure that block transfer data will not write over assigned
timer/counter accumulated or preset values. The file address cannot exceed
address 3577.