Rockwell-automation 1772-LP3 PLC - 2/30 Programmable Controller Progra Manual de usuario descargar pdf (Pagina 184)

Chapter

101

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

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Rockwell-automation 1772-LP3 PLC - 2/30 Programmable Controller Progra Manual de usuario Pagina 184