MD‑SI‑DP1 Communication
‑188‑
terminal resistors are connected correctly, the resistance between A1 and B1 should
be 110 Ω upon power‑off. For devices connected at both ends of the PROFIBUS
network, the communication cables must be connected from their PROFIBUS DP
terminals to the channels marked with "IN" (channels corresponding to A1/B1).
Otherwise, terminal resistors cannot be connected. If any required terminal resistor is
not connected, the communication quality will deteriorate.
The required length of the communication cable between the PROFIBUS DP
expansion card and the PROFIBUS master varies with the baud rate of the master. It is
strictly restricted according to the Siemens DB9 standard. The following table
describes requirements on communication cable length based on the baud rate.
Baud Rate (kbit/s)
Maximum Length of Cable
Type A (m)
Maximum Length of Cable Type
B (m)
9.6 1200 1200
19.2 1200 1200
187.5 600 600
500 200 200
1500 100 70
3000 100
Not supported
6000 100
12000 100
The following table lists the technical specifications of the cables.
Cable Parameter
Type A Type B
Impedance
135 Ω to 165 Ω (f = 3 to 20 MHz) 100 Ω to 130 Ω (f > 100 kHz)
Capacitor < 30 pF/m < 60 pF/m
Resistor
< 110 Ω/km
Not specified
Cross‑sectional area
of conductor
≥ 0.34 mm
2
≥ 0.22 mm
2
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