CC100 Modbus RTU

CODESYS
1

Hello. This is Matthew Kim from Korea.

I would like to contact you because a situation I do not understand occurred while testing the CC100 X11 Modbus RTU.

I connected the CC100 X11 via the PC’s USB 485 port.

I would like to assume that there are no issues with the hardware configuration.

This is because it operates normally when the PC is the Master and the CC100 is the Slave.

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The problem occurs when the CC100 is the Master and the PC is the Slave.

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It displays a “CRC Fail” message and does not work.

As you can see from the communication logs, the CRC is normal, and the two data sets match exactly. It appears as if there is an error in data reception after the CC100 Master has transmitted the data. I have properly configured the termination resistors, with one on the CC100 and one on the USB port.

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There is one more strange phenomenon. When the PC is the Master and the CC100 is the Slave, if I set the parity bit to ODD, there is an intermittent disconnection issue.

I have not made any hardware changes regarding the above settings. I would appreciate it if you could let me know if there are any additional comments or things that need verification regarding this.

2

I apologize.

I have resolved the issue myself.

The manual for the USB to RS485 connector connected to the PC stated that there were no termination resistors, but it appears that a 120-ohm termination resistor is actually installed internally.

Just to be sure, I checked the resistance of the entire line and found it to be around 40 ohms. Since this value is identical to having three 120-ohm termination resistors attached, I removed the resistors and confirmed that it is operating normally.

You can accurately understand it as follows: “The PC converter has strong power (output voltage) so it forced its way through even a 40-ohm ‘crappy’ wire, but the CC100 is precise and strict, yet its signal output is not as strong as a PC’s, so it was crushed by the 40-ohm load.”

I hope this helps those who have experienced the same phenomenon.

Going forward, I plan to re-verify whether D+ and D- reach 60 ohms while not communicating after installing the termination resistors.