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7 PROFIBUS DP Extensions
7.3.2
IsoM (Isochronous Mode)
The IsoM synchronizes DP-Master, DP-Slave and DP-Cycle. The isochro-
nous cycle time starts with the transmission of the SYNCH telegram by the
IsoM master. If the IsoM support of the VPC3+S is enabled, a synchroniza-
tion signal at Pin C4 (SYNC) is generated by each reception of a SYNCH
telegram. The SYNCH telegram is a special coded Global_Control request.
SYNCH
mesage
Figure 7-15: Telegram sequences in IsoM with one DP-Master (Class 1)
Two operation modes for cyclic synchronization are available in the
VPC3+S:
1. Isochronous Mode: Each SYNCH telegram causes an impulse on the
2. Simple Sync Mode: A Data_Exchange telegram no longer causes a
Byte
0
1
Figure 7-16: IsoM SYNCH telegram
Each Global_Control is compared with the values that can be adjusted in
Control_Command_Reg (0Eh) and Group_Select_Reg (0Fh). If the values
are equal a SYNCH telegram will be detected.
70
Cyclic
Cyclic
. . .
Service
Service
Cyclic
Part
SYNC output and a New_GC_Command interrupt. In this mode the
IsoM-PLL can be used for compensation of jitter and loss of synchroni-
zation.
DX_Out interrupt immediately, rather the event is stored in a flag. By a
following SYNCH message reception, the DX_Out interrupt and a
synchronization signal are generated at the same time. Additionally a
New_GC_Command interrupt is produced, as the SYNCH telegram
behaves like a regular Global_Control telegram to the DP state
machine. If no Data_Exchange telegram precedes the SYNCH
telegram, only the New_GC_Command interrupt is generated.
7
6
5
0
0
Group_8
= 1
Revision 1.04
Acyclic
Acyclic
. . .
Service
Service
Acyclic
Part
Cycle Time (T
)
DP
Bit Position
4
3
2
SYNCH
Spare
Token
mesage
Time
Designation
1
0
0
Control_Command
Group_Select
VPC3+S User Manual
Copyright © profichip GmbH, 2012
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