INFICON PSG55x ATM to Medium Vacuum Gauge (Profibus) - Manual (Page 16)

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tira56e1 (2010-02) PxG55x.cp
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
Parameter channel (PKW)
PKE = parameter signature value
IND = index within a slot
res. = reserved
PWE = process value
Standard telegram = cyclic telegram
PKW
= parameter channel (PKE + IND + PWE)
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.
Instructions and responses can’t be blocked: Exactly one instruction is transmitted
in one Output Telegram and exactly one response is transmitted in one Input Tele-
gram. Therefore exactly 4 bytes of user data may be transmitted within one in-
struction or one response.
The instructions / responses are coded in the parameter signature word (PKE):
Bit position
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
AK res. PNU (Parameter Number, Slot)
Where: Bits Meaning
15 … 12 AK ≙ Instruction / response signature
11 … 8 reserved
7 … 0 define the slot from which data are read or onto which a
value is to be written
In Master ⇒ Slave communication, the AK field contains the instruction signature of
the master.
In Slave
⇒ Master communication, the AK field contains the instruction signature of
the slave.
AK Function
Master ⇒ Slave
(Instruction signature)
AK
normal
Function
Slave
⇒ Master
(Response signature)
AK
error
0 No instruction 0 No response
1 Read parameter value 1
2
11
Transmit parameter value
(word)
Transmit parameter value
(double word)
Transmit parameter value
(byte) 7 1)
2 Write parameter value
(data type: word)
1 Transmit parameter value
(word) 7 1)
3 Write parameter value
(data type: double word)
2 Transmit parameter value
(double word) 7 1)
10 Write parameter value
(data type: byte)
11 Transmit parameter value
(byte) 7 1)
1) Instruction cannot be executed (error code)
4.3 Parameter Channel
4.3.1 PKE (parameter
signature value)
Instruction signature