37
Installation and Operation Manual
X-DPT-Profibus-Interface-eng
PN 541-C-068-AAG
November, 2008
Note 1
The readback of a CMD is representing the internal status of the MFC / MFM
which in case of an external analogue VOR command and totalizer reset are
not identical as has been sent via the output data byte. In case of the totalizer
is running and is reset by the output data byte the status is not showing the
reset status but still falls back in the running mode. However this will be
overruled by the constant stream of output bytes.
In a table this is looking as:
Input CMD byte
Output CMD byte
totalizer value
1x
1x
1234.56
1x
2x
0.0
(x = don’t care, can be any value)
Note 2
The totalizer value is not accumulating anymore in case of a ‘valve out of range’
alarm or Valve Override Open is generated. In such case the flow value can be
out of range and not reliable to the totalizer.
Note 3
In case of the valve override function the input command byte is representing
the same value as been sent via the output data byte,
except if the analogue
valve override input is used
. This analogue input has a higher priority above the
valve override command through the profibus. This is done for safety reasons.
So, in this case the input command data is representing the
actual
valve
override status.
Note 4
For all module types the input and output data are defined as consistent data,
meaning that the input or output data stream belongs together and cannot be
split in separate partitions. When using PLC programming software, in most
cases this must be split up by special routines, toherwise this could result in
corrupt and useless data, which can lead to undefined situations.
Example:
When a DP-slave operates in module ‘out[Setp], in[Flow]’, the input and output
stream is only 4 bytes long. Because Siemens S7-300 and S7-400 hardware
are internally 32-bit architectures, you can access the data direct by using
keywords PID and PQD. But in case the DP-slave operates in module type 2 or
3, the data stream is always larger than 4 bytes. This means that you must
use special software routines, supplied by the manufacturer, e.g. Siemens, to
read or write data from or to the slave device.
In the following table the functionality of this command byte is shown. Although
it is one byte with two functions, totalizer and valve override, this byte is
representing two nibbles (4 bits):
•
Low order nibble provides the command ‘Valve override’.
•
High order nibble provides the command ‘Totalizer’.
Function: CMD
type
bit
#
range
[dec]
default
[dec]
options
Valve Override command
0 = Valve Override Off
1 = Valve Open
2 = Valve Close
3 = Valve No Power
4 = Valve Full Power
nibble,
low order 4-bits of byte
0..3
0..5
0
5 = Valve Power Fixed
Totalizer command
0 = Stop totalizer
1 = Run totalizer
nibble,
high order 4-bits of byte
4..7
0..2
0
2 = Reset totalizer