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7.4
DDB Mechanism
The DDB mechanism is enabled in the PROFIBUS mode (XPB/PA = 0) of the
SPC 4-2 with "En-DDB-Mode := 1" (bit 7 in mode register 2). If this bit is not set, all
DDB frames are filtered.
In the PA mode (XPB/PA = 1) of the SPC 4-2, the DDB mechanism is always
enabled, the parameter bit "En-DDB mode" is of no significance in this mode.
With the SPC4/4-1 and SPC 4-2, the DDB mechanism is restricted to the default
SAP. No other SAPs can be operated with DDB. The default SAP is the only SAP
that provides separate resources for the SDN/DDB node table and for reply data
(reply update buffers D, N, U) in the DP mode. If DP-Mode = 0 is set, either the
node table for filtering SDN or DDB response frames or a Reply-on-Indication
buffer for reply data is available to the SAPs even the default SAP.
PROFIBUS Controller SPC 4®-2 LF
C79000-G8976-C157-3
ASIC Interface
85
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