PROFIBUS Termination Resistor is a very important part when setting up a PROFIBUS DP network for Parker controllers/drives such as the DC590P and AC690. If the termination is wired incorrectly, the network may experience communication loss, unstable communication, or the PLC may fail to detect the device.

Parker provides PROFIBUS options for the DC590P and AC690/AC690+ series; among them, the 6055-PROF-00 option is listed by Parker Vietnam for the DC590P and AC690+.

How Are PROFIBUS Termination Resistors Used on Parker DC590P and AC690?

Unlike some newer Parker series that use a PROFIBUS connector with an integrated termination circuit, the PROFIBUS interface on the DC590P and AC690 may require the termination resistor network to be wired according to the standard RS-485 configuration.

A standard PROFIBUS termination consists of:

390 Ω from +5V Bus to line B
220 Ω between line B and line A
390 Ω from line A to GND Bus

This configuration is the standard termination structure used for PROFIBUS DP over an RS-485 transmission line.

Termination Resistor Diagram

             +5V DC
               │
              390Ω
               │
               ├──────── B (B-B')
               │
              220Ω
               │
               ├──────── A (A-A')
               │
              390Ω
               │
             GND

This is the termination at the end of the PROFIBUS line, meaning that not every drive needs to have a termination resistor network installed.

1. Function of the PROFIBUS Termination Resistor

PROFIBUS DP uses the RS-485 communication method. When the signal reaches the end of the transmission line, without proper termination, the signal may be reflected back into the transmission line.

This can cause:

The PLC to lose communication with the drive.
PROFIBUS Slave errors.
The drive to receive commands intermittently.
Unstable data being returned to the PLC.
The network to operate at low baud rates but experience errors when the baud rate is increased.
Random communication errors when a motor or high-power drive is operating.
Communication faults occurring after a period of operation.

Parker also notes in its PROFIBUS documentation that incorrect termination can reduce noise immunity and affect network performance. At the same time, too many termination resistors can reduce the signal level on the bus.

2. PROFIBUS Pins on DC590P and AC690

According to the PROFIBUS communication wiring diagram, the key signals include:

Pin	Signal	Function
1	0Vext	External 0V supply
2	+5V DCext	+5V
3	B-B’	PROFIBUS Data B
4	A-A’	PROFIBUS Data A
5	RTS	Request To Send
6	GND	Ground

Among these, pins 3 and 4 are the two main PROFIBUS data lines.

When implementing the termination, the three resistors are connected as follows:

+5V → 390 Ω → B → 220 Ω → A → 390 Ω → GND

3. How to Wire the PROFIBUS Termination Resistor for DC590P

Assuming the system is configured as:

PLC/SCADA → DC590P #1 → DC590P #2

the device located at the end of the PROFIBUS line must have the termination enabled.

4. Do Not Confuse DC590P/AC690 with AC20/AC30

This is a very important point when working with Parker systems.

The 390 Ω – 220 Ω – 390 Ω direct wiring configuration should not be mechanically applied to all Parker series.

Parker Series	PROFIBUS	Termination Method
DC590P	PROFIBUS option available	According to the PROFIBUS interface/connector
AC690	PROFIBUS option available	According to the PROFIBUS interface/connector
AC20	Communication option available	Depending on the module/connector
AC30	PROFIBUS option available	Depending on the module/connector

Parker currently provides different communication options for the DC590P, AC690, AC20, and AC30. Therefore, the correct communication option and connector for each model must be checked before wiring.

In particular, when AC20 and AC30 use a PROFIBUS connector with an integrated termination circuit, the implementation will be different from manually wiring three separate resistors as shown in the DC590P/AC690 diagram above.

5. Some PROFIBUS Errors Caused by Termination

Error 1: PLC Cannot Detect the DC590P/AC690

Check:

PROFIBUS cable.
Whether the A/B lines are wired correctly.
Whether the shield is properly connected.
Slave address.
GSD file.
Termination at both ends of the network.

Error 2: PROFIBUS Communication Works Intermittently

This is a case where the termination should be checked carefully.

Possible causes include:

Missing termination.
Termination installed at the wrong location.
Too many termination resistors.
Poor connector contact.
Poor shielding.
PROFIBUS cable routed close to the drive power cables.
Cable length exceeding the limit for the selected transmission speed.
Noise from the power system.

Error 3: A/B Are Wired Correctly but There Is Still No Communication

Do not check only A/B.

You should also check:

A/B + GND + termination + shield + connector.

Especially in systems with multiple drives, the PROFIBUS cable shield must be connected correctly to minimize the effects of electromagnetic interference.

6. PROFIBUS Wiring Checklist for DC590P and AC690

Before powering up and commissioning the system, the following checklist can be used:

① Check the PROFIBUS cable

Use the correct PROFIBUS DP cable.
Correct A/B wiring.
Do not reverse the polarity.

② Check the shield

The shield is properly grounded.
Avoid routing it in parallel with power cables.

③ Check the termination

First end: ON
Middle nodes: OFF
Last end: ON

④ If using separate termination resistors

Check:

390 Ω → +5V ↔ B
220 Ω → B ↔ A
390 Ω → A ↔ GND

⑤ Check the PLC configuration

Correct GSD.
Correct PROFIBUS address.
Correct transmission speed.
Correct module/PPO or process data configuration, depending on the option.

Conclusion

The termination resistor is a small detail but has a major impact on the stability of a PROFIBUS network. When implementing PROFIBUS for Parker DC590P and AC690, it is necessary to correctly identify the two physical ends of the bus and implement termination at these two ends.

For a termination configuration using separate resistors, the basic arrangement is:

390 Ω – 220 Ω – 390 Ω

corresponding to:

+5V → B → A → GND.

Missing termination can cause signal reflections and communication errors, while too many termination resistors increase the load on the transmission line and reduce the signal level. Therefore, the most important principle is: termination should only be enabled at the two ends of each PROFIBUS RS-485 bus.