Rockwell Automation 1747-BSN Backup Scanner Module - Manual (Page 128)

Publication 1747-UM010B-EN-P - September 2003
7-16 RIO Block Transfer
Instruction Operation
1. The scanner processes the BTR/BTW when it detects that the
SLC control program rung, which contains the BTR/BTW, goes
true.
If the RIO scanner detects any problem at this point (such as
invalid block transfer control field, or unconfigured device), the
control structure word 2 fills with the error code and the ER bit
(bit 12) is set. If no problems occur, the EW bit (bit 10) and ST
bit (bit 14) are set in the control block.
The SLC control program can monitor the block transfer by
examining bits in word 0 of the control block. They indicate
when the scanner has started processing (EW and ST) the block
transfer and whether the block transfer operation completed
successfully (DN) or failed (ER). The SLC control program can
take different actions based on these status bits.
2. When a block transfer completes successfully, the DN bit is set.
This indicates that the block transfer control block has been
updated with the actual transmitted word count. This is
important for BTR instructions, because this indicates the
number of valid data words received from the remote device.
This data is stored in the BTR data file.
3. If the block transfer fails, the length field and the data file are
not updated. The ER bit is set and the error code field indicates
the problem.
4. The SLC control program must indicate to the scanner when it is
done processing the status word in the control structure
(because DN or ER was set) so the corresponding control bits
can be reused for another block transfer operation. The SLC
control program indicates that it is done processing the block
transfer when it solves the BT rung false, which clears the EN bit
in the control block.
TIP
The ST bit is not set if the scanner is already in the
process of block transferring data to a location
within the same logical RIO rack. The ST bit is set
only after any previous pending block transfers to
the same logical rack are completed and the block
transfer request is scheduled on the RIO link.