Instruction Operation - Allen-Bradley SLC 500 Series Reference Manual
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Also See for SLC 500 Series:
- Manual (270 pages) ,
- Quick start manual (70 pages) ,
- Migration manual (60 pages)
Table of Contents
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 ST bit is not set if the scanner is already in the
TIP
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.
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.
5. When the RIO scanner detects that the EN bit cleared, it then clears the
EW, ST and DN or ER bits, as well as the Transmitted Word
Count/Error Code. This ensures that the status bits in the control block
are not reflecting the results of the previous block transfer operation.
Block Transfer Instructions
Publication 1747-RM001G-EN-P - November 2008
8-7
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