Block Transfer Timing Diagrams - Allen-Bradley 1747-SN User Manual

5–14 RIO Block Transfer
Publication 1747 6.6 - July 1996
Your SLC control program can monitor the block transfer by
examining the M1 status flags. They indicate when the scanner
has started processing (EW and ST flags) the BT and whether the
BT operation completed successfully (DN flag) or failed (ER
flag). Your SLC control program takes different actions based on
these status flags.
4. If the BT completes successfully, the scanner fills in the M1 BT
length status field. If it was a BTW operation, the BTR data area
of the M1 BT buffer is not updated. If it was a BTR operation, the
new BTR input data (based on length) is placed in the BTR data
area of the M1 BT buffer and the unused buffer area clears. The
DN status flag then sets to indicate to the SLC control program
that the BT operation completed successfully and that the M1
input status buffer has been completely updated.
5. If the BT fails, the length field and BTR data area are not updated
(length remains cleared). The error code field indicates the
problem type. The ER flag sets to indicate to the SLC control
program that the BT operation was unsuccessful.
6. The SLC control program must indicate to the scanner when it is
done processing the M1 input/status buffer (because DN or ER
was set) so the corresponding M0 output/control buffer can be
re-used for another BT operation. The SLC control program
indicates that it is through processing when it clears the EN flag.
7. When the RIO scanner detects that the EN flag has been cleared
by the SLC control program, it then clears the EW, ST and DN or
ER flags. This ensures that the status flags in the M1 input status
buffer are not reflecting the results of the previous BT operation.
Note that the other M1 BT Status buffer fields, such as length,
error code, and BTR data are not cleared when the scanner clears
the status flags. These fields are only updated when the scanner
has processed a BT operation as indicated by the DN or ER flag.
For example, if there was a problem with a BT operation, the
error code will remain in the M1 BT buffer until the next BT
operation causes it to be changed (cleared if DN is set or an error
code if ER is set). Therefore, the SLC control program should
precede the examination of the error code field with the ER flag.

Block Transfer Timing Diagrams

The following pages contain timing diagrams that illustrate the
effects of different control flags on a BT operation.