Profichip VPC3+S - Isom (Isochronous Mode)

7 PROFIBUS DP Extensions
70
Revision 1.04
VPC3+S User Manual
Copyright © profichip GmbH, 2012
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.
Cyclic
Service
Cyclic
Service
Acyclic
Service
Acyclic
Service
Token
Spare
Time
. . .
. . .
SYNCH
mesage
SYNCH
mesage
Cycle Time (T
DP
)
Cyclic
Part
Acyclic
Part
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
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.
2. Simple Sync Mode: A Data_Exchange telegram no longer causes a
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.
Byte
Bit Position
Designation
7
6
5
4
3
2
1
0
0
0
0
0
Control_Command
1
Group_8
= 1
Group_Select
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.