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Windows 8 and U90Ladder

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This is my first topic in this forum I have question about U90 Ladder and windows8. I cannot connect my Laptop to Unitronics M91-2-R34 (checked all possible variations of ports, baud rates, stop bits and so on). User Account Control (UAC) settings is turned off. I am using Prolific USB to Serial converter. This converter can work with windows 8. Is U90 Ladder working with windows 8? Perhaps somebody can help for me...


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Dear Sir,

Thank You for quick answer.

I am using 64 bits version of Windows 8. I am reinstalled prolific driver (from https://unitronics.exavault.com/share/view/1j3m-glck37nv-1lljo5h ) as You recommended, but situation is the same.

In the Device Manager, Prolific USB-to-Serial Com Port (COM5), set correct. When I checked with "Check PL-2303 chip version v1002" com port 5 I get: This is a PL-2303 RA chip.

In the U90 Ladder I set Baud rate-9600, Parity-None; Stop Bits-1; Data Bits-8 and Flow Control- None, com 5 (the same configurations are in Prolific settings).

Then I trying to get PLC settings, I am got error- (2) U90Ladder:

Communications could not be established due to one of the following:

*Cable connections are not secure.

*Timeout is too short.

Incorrect communication settings.

Check your cables and communication settings and try again.


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  • 2 years later...
  • 5 months later...

Are you certain that the issue is not with your Profilic drivers?

They have to be old ones from 2008.


Look at this video here:


The download link to old drivers is in the description.

Apparently they decided to disable support for Windows 8+ so that people would buy new cables but fortunately old drivers still work with Windows 8 and 10.


U90 works nicely on my Win8.

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