Communicating with Remote I/O

6-17

 

 

Block-Transfer Sequence with Status Bits

Start

ladder logic

The following figure describes the different states of the block-transfer status bits.

Detects that a rung containing a block-transfer is enabled and sets the enable .EN bit and resets the .ST, .DN, .ER, and .EW status bits.

The processor sends the block-transfer request to the I/O scanner, sets the .EW bit, and resumes the program scan.

Executes block-transfer asynchronously to the program scan

I/O scanner

A

 

 

 

 

 

 

 

 

 

yes

 

 

Does this slot address

 

 

 

 

 

 

 

The scanner place the request

have a BT in process?

 

 

 

 

 

 

in the waiting queue.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

no

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Is an active buffer available?

 

no

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

yes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

no

 

 

 

 

 

 

 

 

 

 

 

 

Is the request a BTW?

 

The scanner sets the .ST status

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

bit and starts the watchdog timer.

 

 

 

 

 

 

 

 

 

 

 

yes

The scanner accesses the BTW file in the data table and copies the data to the active buffer.

Transfers the block-transfer request to/from the I/O chassis.

 

 

no

Does the module respond?

 

C

 

 

 

see page

 

yes

6-19

 

 

 

 

 

 

 

 

Bsee page 6-18

Publication 1785-UM012D-EN-P - July 2005

Page 88 Page 90
Page 89
Image 89
Bradley Smoker PLC-5 Block-Transfer Sequence with Status Bits, Yes Does this slot address, Does the module respond?
Page 88 Page 90
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