INFICON SKY CDGxxxD (Profibus) - Manual (Page 13)

tira54e1-a (2009-01) CDGxxxD.cp
13
Within the DataExchange mode the DP-master class 1 cyclically transmits and
requests data from all configured slaves in the network. This data transfer aims at
the fast propagation of measurement data and command data within the system.
The next two figures contain the input and output data of the Profibus device. The
data are divided between a parameter and a process data part.
The parameter data area contains a dedicated channel called parameter channel. It
allows the transmission of cyclic requests by specifying an additional protocol within
the input and output data area. A concise description can be found in section 5.3
"Parameter channel".
The process data contain the measurement and command data as described in
section 5.4 "Process data".
The Input Area (DxIn) as sent in the DataExchange telegram (transmitted by the
CDGxxxD) consists of the 8 byte parameter channel (if there is a parameter chan-
nel in the telegram) and up to 8 byte of process data. The actual amount of process
data is determined by the board configuration of the basic device.
Octets
0…7
Octets
8…15
Parameter channel Process data
The Output Area (DxOut) as received in the DataExchange telegram (transmitted
by the master) contains the 8 byte parameter channel.
Octets
0…7
Parameter channel
The parameter channel was created as a means to transmit acyclic requests within
a cyclic data stream. Within this section a brief introduction into the matter is
provided. The following table exhibits the principle structure of the parameter chan-
nel.
Octets Octets
0 1 2 3 4 5 6 7 8 9 10 11 12 13 …
PKE IND res. PWE Standard telegram
PKW
PKE = parameter signature
IND = index within a slot
res. = reserved
PWE = process value
Standard telegram = cyclic telegram
PKW = Parameter signature / value
The PKW allows a read and write access to the parameter space of the slave.
Within the PKW mechanism the master formulates an instruction. The slave pro-
cesses the instruction and formulates the response.
4.2 Cyclic Data Telegrams
in Data Exchange Mode
Input data
Output data
4.3 Parameter Channel
4.3.1 PKW