Rockwell Automation 1785 PLC-5 Manuel d'utilisateur télécharger pdf (Page 114)

Transferring Discrete and BlockTransfer Data

Chapter 8

8-19

BlockTransfer Sequence

Figure 8.11 shows the sequence the processor follows to run a block

transfer.

Figure 8.11

BlockTransfer

Sequence

Q17 Buffer

for 17 BT

Requests

3a, 3b, 5

Active BT

area

4a, 4b I/O Chassis

1, 7

Ladder

Program

6 STI

Data

Files

Request

Priority Request

Data

Request and Outgoing Data

Acknowledgement

and Incoming Data

1. Ladder logic enables the block transfer.

2. The processor places the blocktransfer request in the queue, or in the active buffer if the queue is empty. If the queue is full, the

request is ignored until the next scan.

3. If the block transfer is a:

BTW: The processor interrupts the program scan momentarily to transfer data from the BTW file to the active buffer. The active

buffer transfers the request and outgoing data to the processorresident local I/O module or to the remote I/O adapter.

BTR: The active buffer sends the blocktransfer request to the processorresident local I/O module or remote I/O adapter. In

the same local blocktransfer update or in the next remote I/O scan, the active buffer receives the blocktransfer

acknowledgement and incoming data.

Important

: The processor interrupts the program scan momentarily to transfer incoming data to the BTR file one word at a

time; therefore, some ladder logic could execute in between word transfers to the BTR file. We recommend that you buffer your

BTR data with a filetofile move or a copy instruction using a BTR done bit to condition the rung if you need file integrity of

the data.

4. If the block transfer is to:

ProcessorResident Local I/O: The processor continuously runs blocktransfer requests for all processorresident local I/O

modules in the order the processor queues the requests.

Remote I/O: The processor runs one blocktransfer request for one blocktransfer module per rack address per remote

I/O scan.

5. The processor clears the active buffer and the active buffer accepts the next request after the buffer receives a confirmation of a

valid read or write.

6. When the processor enables a fault routine or STI, the processor runs any blocktransfer program in the fault routine or STI ahead

of any blocktransfer requests in the queue, as soon as the active buffer completes any block transfer currently in the active buffer.

The program scan is stopped until the STI or fault routine block transfer is complete.

7. The blocktransfer process runs asynchronously to the program scan, so data can change during program scan.

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Rockwell Automation 1785 PLC-5 Manuel d'utilisateur Page 114

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