Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 156)

Chapter
14
14-1
Block Transfer
This chapter describes three types of block transfer:
read
write
bidirectional
Block transfer is a combination of an instruction and support rungs used to
transfer up to 64 16-bit words of data in one scan from I/O modules
to/from the data table. This transfer method is used by intelligent I/O
modules such as the analog, PID, servo positioning, stepper positioning,
ASCII, thermocouple, or encoder/counter modules.
Block transfer can be performed as a read, write, or bidirectional operation,
depending on the I/O module you are using. An input module uses the
read operation, an output module uses the write operations. During a read
operation, data is read into the data table from the module. During a write
operation, data is written to the output module from the data table.
The processor uses two I/O image table bytes to communicate with block
transfer modules. The byte corresponding to the module’s address in the
output image table (control byte) contains the read or write bit for initiating
the transfer of data. The byte corresponding to the module’s address in the
input image table (status byte) is used to signal the completion of
the transfer.
Important: Do not use word 127 for data storage.
Whether the upper or lower byte of the I/O image table word is used
depends on the position of the module in the module group. When in the
lower slot, the lower byte is used and vice versa (Figure 14.1).
Chapter Objectives
Basic Operation