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Entry/Exit Check of an MDS in an SLG Field
6.6
Diagram showing possible MDS states on an SLG
Notes for the understanding and use of the following diagram
The following section describes all types of status which are important for correct
processing. The significance of the remaining types of status will be self-evident
from an understanding of those described here.
The source point of all considerations is the RESET command. In principle, this
can be issued if:
S there is no MDS in the SLG transmission window. Status 11 is then valid, i.e.
"MDS not present, Next MDS bit set, command not present".
Note
The "Next MDS bit" is set in the filehandler since the NEXT function is
implemented in the RESET command (MDS_IO_control 0 only). The "Next MDS
bit" is not set in the case of MDS_IO_control 1 or MDS_IO_control 4. Status 5 is
then valid, i.e. "MDS not present, Next MDS bit not set, command not present".
S an MDS (old or new) is in the MDS field. Status 3 is then valid, i.e. "old/current
MDS present, Next MDS bit not set, command not present".
Note
The "Next MDS bit" is not set, since the filehandler always considers the MDS,
which is present when the RESET command is issued, the old/current MDS
(whether it is new or old) and thus resets the "Next MDS bit".
In status 11 the following can occur.
S a new MDS enters the transmission window. Since the Next MDS bit is set, this
MDS immediately becomes the old/current MDS and the Next MDS bit is reset.
Status 3 is valid.
S an old MDS enters the transmission window. Since the Next MDS bit is set
(processing of the old MDS is terminated), no further command can be issued
to this MDS. Status 9 is valid.
S a NEXT command is issued by the FC 56. Since the Next MDS bit is already
set, the filehandler remains in status 11.
S a command is issued by the FC 56. No MDS is present, the Next MDS bit is set
(do not process this command until the next/new MDS). The command is
temporarily stored by the filehandler. Status 23 is valid.
6-6
FC 56
J31069-D0155-U001-A0-7618
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