Rs485 Transmission Mode - Emerson Bettis XTE3000 Installation, Operation And Maintenance Manual

Section 4: PROFIBUS DP Description
March 2022
4.1

RS485 Transmission Mode

The PRO2000v4_RED module uses a half-duplex, multidrop, serial communication line RS485. The
card communicates with the Masters via its RS485 interface and the transmission media consists in a
shielded twisted pair cable. Transmission speed from 9.6 kbit/s to 1.5 Mbit/s are available. One unique
transmission speed is allowed for all devices on the bus when the system works.
All devices are connected in a bus structure. Up to 32 station (Master and Slaves) can be connected
in one segment without repeaters. Repeaters can be used to extend the number of device up
to 126 and to enlarge the network area. Table 1 shows the relationship between baud rate and
segment length.
Table 1.
The bus must be terminated by an active bus terminator at the beginning and at the end of each
segment. Only two terminations in one bus segment must be provided. To ensure error-free
operation, both bus terminators must be powered. The maximum cable length depends on the
transmission speed. Cable lengths indicated in Table 1 are based on type A cable, as specified by the
EN 50170, having the following characteristics.
•
•
•
•
•
The use of cable of previously used type B is not recommended.
The data lines must not be reversed. Use of shielded cable is mandatory for having high system
immunity against electromagnetic disturbs. The shield should be connected to ground on both
sides. The data lines should be kept separate from all other cables. It should be laid in separate,
conductive and earthed cable trunking. It must be ensured that there are not voltage differences
between individual nodes of PROFIBUS DP.
6
Baud Rate
9.6 K
19.2 K
45.45 K
93.75 K
187.5 K
500 K
1500 K
Impedance from 135 to 165 ohm
Capacity < 30 pF/m
Loop resistance 110 ohm/km
Wire gauge 0.64 mm
Conductor area > 0.34 mm
Installation, Operation and Maintenance Manual
Maximum Segment Length (no repeater)
2
MDE 256 Rev. 1
1,200 m
1,200 m
1,200 m
1,000 m
1,000 m
400 m
200 m
PROFIBUS DP Description