P30P-09A 48 User's manual
to exchange information between devices via a serial link.
5.9.1 Connection of the serial interface
RS-485 standard allows for a direct connection of up to 32 devices on a single serial link with
a length up to 1200 m (at baud rate 9600 b/s). It is necessary to use additional intermediate-separation
circuits for connecting higher number of the devices, for example PD51 manufactured by LUMEL S.A.
Output of the interface line is shown in Fig. 3. To obtain the correct transmission it is
necessary to connect the lines A and B in parallel with their equivalents in other devices. The connection
must use a shielded wire. The cable shield should be connected to the protective terminal in close
proximity to the transmitter (connect a shield to the protective terminal at one point only).
GND line serves as the additional security device in case of significant connection line length.
In such case, GND signals of all RS-485 bus devices should be interconnected.
RS-485 interface card or the converter is required for a connection to a PC, for example PD51
or PD10. The method of connecting devices is shown in Fig. 21.
Fig. 21 Connecting the RS-485 interface.
Transmission line markings for the PC cards may vary depending on the card manufacturer.
5.9.2 Description of the MODBUS protocol implementation
The implemented protocol is compliant with the PI-MBUS-300 Rev G specification of Modicon.
Overview of P30P transducer MODBUS protocol serial port parameters:
●
Transducer address 1..247.
