Chapter
10
101
Block Transfer
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. It is used with intelligent I/O modules such as the
analog, PID, servo positioning, stepper positioning, ASCII, thermocouple,
or encoder/counter modules which have this capability. Block transfer can
be compared to single transfer programming in which only one word of
data is transferred per scan.
Block transfer can be performed as a read, write or bidirectional operation,
depending on the I/O module being used. An input module uses the block
transfer read operation, an output module uses the block transfer write
operation and a bi-directional module can use both the read and write
operations. During a read operation, data is read into the processor’s
memory from the module. During a write operation, data is written to the
output module from the processor’s memory.
The processor uses two (2) 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.
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 10.1).
10.0
General
10.1
Basic Operation
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
