Technical data

MESOMATIC Automation und Messtechnik GmbH D-71394 Kernen
4. The Profibus-DP interface
4.1. Connection
The bus connector of the Profibus interface has been designed as a 9 pole SUB-D socket in
accordance with Profibus standard DIN EN 50170. The socket has been installed in the front
panel of the DK900, and been marked “X6”.
A bus plug is used to connect the bus cable with the DK900. The design of the bus plug
(internally through-wired data connector) ensures the trouble-free connection and/or
disconnection of the DK900 during running operation without affecting any other bus
participant. Bus plugs of several protection classes and several types of construction,
with or without a terminating resistor are commercially available.
The bus plug to be mounted on the cable side is not
included in the DK900’s scope of
supply!
The pins of the 9 pole SUB-D socket have been allocated in accordance with DIN EN 50170 as
follows:
X6 pin Signal Description
1 Shield Shield / signal earth (identical with connector flange)
2 M24
Open, not allocated
3 RxD/TxD-P Receive/transmission data - Plus
4 CNTR-P Repeater control signal
5 DGND Reference ground
6 VP +5 V supply for terminating resistors
7 P24
Open, not allocated
8 RxD/TxD-N Receive/transmission data - Minus
9 CNTR-N
Open, not allocated
If devices are used the baud rates of which exceed 1.5 MBaud it must be ensured, due to the
participant’s capacitive load and the line reflection generated thereby, that the connector
plug to be mounted on the cable side is provided with integrated series inductances.
If the baud rates exceed 1.5 MBaud no stubs must be connected to the DK900! A stub is
defined as the connecting line between the connector plug and the field device (DK900).
Experience has shown that stubs are permissible for very low baud rates (up to 93.75 kBaud)
only. Thus the total stub length, which is determined by adding the individual lengths of
all stubs installed, must not exceed 6 meters, for example, if the baud rate amounts to
93.75 kBaud and a category A cable (30 pF/m) is used. If, in exceptional cases, the
installation of stubs is unavoidable, these must not be equipped with a bus terminator.
The bus cable is match-terminated (in its impedance) by bus terminating resistors which are
installed at both cable ends. The provision of 3 individual resistors as prescribed by DIN
EN 50170 ensures that
· the line is set to a defined steady state potential;
· line reflections are minimised;
· the bus is set to an almost constant load behaviour.
4.2. Parameterisation of the DK900
4.2.1. Profibus parameters
The 3 digit Profibus address must be entered in the DK900 since it does not allow to be
edited via the Master. The address is communicated to the DK900 Profibus controller via the
DK900’s internal serial interface. As soon as the entry of a new Profibus address is
completed, the DK900 logs out of the Profibus and tries to get in contact with the Profibus
Master via the new Profibus address.
Profibus communication is impossible until the DK900 has started, i. e. until measuring
values appear in the display.
The DK900 Profibus controller is provided with an automatic baud rate detection feature and
supports baud rates from 9.6 kBaud up to 12 MBaud.
DK900 8