Rockwell Automation 1747-SN Remote I/O Scanner - Manual (Page 86)

Publication 1747-UM013B-EN-P - January 2005
5-8 RIO Block Transfer
Successful Block Transfer Read/Write
The illustration on the previous page shows a successful BT
operation.
1. The SLC control program copies new data to the data file (BTW
only) and solves the BT rung true, which sets the enable (EN)
bit.
2. The scanner detects that the EN bit is set, validates the control
block information, puts the BT request on the RIO link
successfully, and since no other BTs are pending for the same
logical rack, sets the enable waiting (EW) and start (ST) bits.
3. The scanner receives a BT reply (with no errors) from the RIO
link device, copies the received data to the data file (BTR only)
and sets the done (DN) bit.
4. The SLC control program detects the DN bit, processes the BTR
data and solves the BT rung false, which clears the enable (EN)
bit.
5. The scanner detects that the SLC control program has completed
processing (because the EN bit is clear) and clears the EW, ST
and DN bits. At this point, the SLC control program could
re-initiate the same BT operation by solving the BT rung true
again.
TIP
Except for the time-out bit, TO (bit 08), do not
modify any controller status bits while the block
transfer is in progress.
IMPORTANT
The BTR/BTW instruction must be scanned (true or
false) in order to update the control and status bits.