KROHNE ALTOSONIC V Modbus EN - Manual (Page 24)

ALTOSONIC V
ModBus Manual 0300 rev07 E 7.30855.35.00 Page 24 of 64
7.3.4 The UFP-V as Master
The master mode is activated when the parameter 5.1 MODBUS_DEVICE_TYPE=2.
For master mode the UFP-V must know what it should send to the connected slave device, therefore
the master works with poll blocks. Each poll block defines how a transaction should take place i.e.
which slave is addressed, which registers are read or write and how to do it.
The maximum number of poll blocks to define is 20. The number of poll blocks to use is set with the
parameter 7.1 NUMBER_OF_POLLBLOCKS_TO_USE.
During start-up of the UFP-V, a poll block validation check will be done. Only the number of poll blocks
defined in 7.1 NUMBER_OF_POLLBLOCKS_TO_USE will be checked.
The maximum response time after a poll block request is set by the parameter
7.2 REQUEST_TO_RESPONSE_TIMEOUT.
If no response is received from the slave within this time, a poll block timeout error is generated.
So for every pollblock (=data movement) set :
•
The 7.3a SLAVEID : the address of the slave device , notice that 0 is a broadcast to all slaves, not
all the functions are allowed with broadcast messages.
•
The 7.3b MASTER REGISTER, this is the location of the data in the UFP-V.
• The 7.3c SLAVE REGISTER, this is the location of the data in the slave device.
•
The 7.3d N_POINTS, this is always the number data points of the specific datatype to transfer, like
1 Boolean, 1 int, 1 float. The real number of 16 bit registers in the Modbus message is calculated.
For instance, in modicon compatible mode the number of registers in the message is always 2
times the number of floats.
In not-modicon compatible mode the number of registers in the message is always the same as
number of floats. So number of points in the pollblock definition always count the datatypes.
• The 7.3e FUNCTION selects which Modbus function is used for the data transfer (see a complete
list in the manual).
•
The 7.3f DATATYPE is for internal validation only but should be filled in correctly.
• The 7.3g DATANOTATION defines in which byte-order the data is send, float, longs, doubles may
be send with different notations (like big and little indian).
•
The 7.3h DELAY is the time to wait after the last pollblock has been send before sending the next
pollblock. When all the pollblocks are defined, select with
7.1 NUMBER_OF_POLLBLOCKS_TO_USE, which pollblocks to use. 1=first one only, 2 is
number one and two …and so on.