Direct Communication problems

If your PC is not able to establish direct communications with a locally connected PLC, refer to the following table:

Problem	Possible Cause	Recommended Action
No Communications	PLC is not turned on	Turn the PLC on. If the PLC does not turn on, click here.
	Communication cable	Check that: You are using the correct communication cable. The RS232 port of the PLC is connected to your PC's communication port according to the instructions in the product's User Guide.
	Communication settings	Refer to Communications Settings.
		If you are trying to communicate with an M90 network via a bridge, you must define your project as a Network project--however, U90 Ladder cannot automatically detect communication settings in a Network project. Make sure the current RS232 parameters in your project are the same as the parameters that are actually in the bridge. Remember: to download via an M90 bridge to a networked M90, you must select the unique ID of the networked M90.
	COM port is not enabled	Check that your PC communication port is enabled. This means checking your PC's BIOS/CMOS setup.
	COM port is defective	Refer to How do I use a PC to access an M90 via GSM modem?
	COM port is occupied	Close the application that is accessing the port. For more information, refer to How do I use a PC to access a PLC via GSM modem?

If you are still unable to establish communications:

Contact your local Unitronics distributor.