VLT
®
5000/5000 Flux/6000 HVAC/8000 AQUA PROFIBUS
MG.90.D1.02 – VLT is a registered Danfoss trademark
13
■ PCA processing
The master controls and monitors VLT parameters
through the PCA portion of the PPOs type 1, 2 and
5 and requests a response from the VLT (slave). In
addition to the parameter processing, the VLT can
also transmit a spontaneous message.
Requests and responses involve an acknowledge-
ment exchange (a so-called handshake) which
cannot be worked off in stack operation. This
means that the master, when sending a read/write
request, must wait for the response before sending
a new request. A request or response is limited to
a maximum of 4 bytes, i.e. no text strings can be
transmitted.
PCA - Parameter description
Request and response
In the RC portion of the PCA word the requests of
the master to the slave are triggered. The other two
PCV fields IND and PVA must be evaluated as
well.
The PVA portion transmits parameter values in
word size with the bytes 7 and 8; double words
require the bytes 5-8, i.e. 32 bits.
If the request or response contains array elements,
the array subindex will be in IND (byte 3). In the
event of a parameter description, IND contains the
record subindex.
RC content
Request Function
0 No request
1 Request parameter value
2 Change parameter value (word)
3 Change parameter value (double word)
4 Request description element
5 Change description element
6 Request parameter value (array)
7 Change parameter value (array word)
8 Change parameter value (array
double word)
9 Request number of array elements
10-15 Not assigned
PCA interface
Response Function
0 No response
1 Transmit parameter value (word)
2 Transmit parameter value (double
word)
3 Transmit description element
4 Transmit parameter value (array word)
5 Transmit parameter value
(array double word)
6 Transmit number of array elements
7 Request not executable (with error
number, see below)
8 No operating authority for PCV inter-
face
9 Spontaneous message (word)
10 Spontaneous message (double word)
11 Spontaneous message (array word)
12 Spontaneous message (array double
word)
13-15 Not assigned
If a request from the master is not executed by the
slave, the RC word in the PPO-Read has the
value 7. The error number is in bytes 7 and 8 of the
PVA element.
Error no. Meaning
0 Improper PNU
1 Parameter value not changeable
2 Upper or lower value passed
3 Faulty subindex
4 No array
5 Wrong data type
6 Setting not permitted (resettable only)
7 Description element not changeable
8 No PPO-Write for IR
9 Description data not available
10 Access group
11 No parameter operating authority
12 Keyword missing
13 Text not readable in cyclical traffic
14 Name not readable in cyclical traffic
15 Text array not available
16 PPO-Write missing
17 Request temporarily unexecutable
18 Other error
19 Data not readable in cyclical traffic
RC: Request/Response Characteristics (Sector: 0-15)
SPM: Toggle bit for spontaneous messages
PNU: Parameter Number (Sector: 1-990)
151413 12 11 10 9 8 76543210
RC MSP PNU
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