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Request frames at a SAP other than the DEFAULT SAP are accepted only if the
SSAP is different from the DEFAULT SAP. The request SSAP must have suitable
parameters assigned by the FLC. The received data are entered in the indication
queue. As the reply, the data from the reply update buffer pointed to by the Reply-
Update-Ptr of the addressed SAP are sent. If the received request data are entered
in the indication queue, the "IND-WP-PRE" pointer is set to the next free segment
and the "IND-PRE" interrupt is generated. If the job is completed, the IND-WP
pointer is also set to the next free segment and the "IND" interrupt generated
(indication).
Swap Buffer Principle
Figure 6-1
The SPC 4-2 enters error-free output data received from the DEFAULT SAP of the
DP master at the local DEFAULT SAP in the indication buffer D. The SPC 4-2
generates the "Watchdog Reset" interrupt. Following this, the SPC 4-2 swaps the
indication buffers D and N either immediately (DIAG.SYNC mode = 0) or at the
next "Sync" command (DIAG. SYSNC mode = 1). After swapping the indication
buffer pointers D and N, the SPC 4-2 sets the IND-N-Valid = 1 flag in the default
SAP and generates the "Output Data Exchange" interrupt. These actions are
executed with the lock active to ensure data consistency. If the FLC wants to
update its output data in the indication buffer U, it must first check whether IND-N-
Valid = 1 is set (in other words, whether valid output data are entered in indication
buffer N). If this is the case, the FLC can update its output data by swapping the
indication buffers N and U. The FLC must also reset the flag IND-N-Valid = 0 in the
DEFAULT SAP. These actions must be performed by the FLC with lock active.
The FLC puts together the input data in the reply update buffer U and then swaps
the U buffer with the reply update buffer N.
The FLC must also set the flag RUP-N-Valid = 1 in the DEFAULT SAP if the reply
update pointers U and N are swapped. These actions must be performed by the
FLC with lock active. If the DP master requests input data using a request frame,
the SPC 4-2 replies
PROFIBUS Controller SPC 4®-2 LF
C79000-G8976-C157-3
Swapped
b
by SPC 4
Buffer
D
Swap Buffer Principle
Swapped
by FLC
Buffer
N
DP Interface
Buffer
U
53
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