Burkert Type 8056 - Manual (Page 104)

- 104 - RS232_485_ETP_MODBUS_BU_REV02.doc
6.2.2. CONNECTING THE CONVERTER TO AN RS485 NETWORK
This network is comprised of a certain number of devices each characterised by a univocal address number (for
convenience we shall call this type of appliance “SLAVE”), and by a single referee ("MASTER") that interrogates all of
the instruments connected in turn: a maximum number of 32 devices can be connected.
Example of connection in an RS485 network:
o~~~~~o~~~~~~o~~~~~~o~~~~~~o~~~~/....../~~~~o~~~~~~o Terminal (+)
| | | | | | |
D0 D1 D2 D3 D4 D30 D31
| | | | | | |
o~~~~~o~~~~~~o~~~~~~o~~~~~~o~~~~/....../~~~~o~~~~~~o Terminal (-)
D0÷D31 = devices connected (any of them may be the network master).
6.2.3. CRITERIA FOR DATA EXCHANGE
Information requests sent from the MASTER are received contemporaneously by all the SLAVES, but only the one
addressed replies. For this reason, it is absolutely necessary for all the SLAVES to have different addresses.
The MASTER establishes the time scheduling with which the information must transit and must therefore be the single
type of this element in the network; two MASTER would create conflicts in the communication, making the entire
system unusable.
6.2.4. TYPES OF DEVICE FOR THE NETWORK CONNECTION
MASTER type devices can be PCs, PLCs or other terminals that collect measurement data from the instruments.
SLAVE type devices on the other hand are the Millennium series converters.
6.2.5. EXTENDING THE NETWORK
When more than 32 instruments have to be connected, these must be divided into separate groups of a maximum of 32
devices. Each group connects to the next through a repeater which has the task of regenerating the necessary electric
signals. In any case, given that the maximum number of addresses that can be assigned for the instruments of the
Millennium series is 256, networks with more than 256 elements cannot be created.