RS232 Hardware Flow Control in Windows 7

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jkeogh
Posts: 7
Joined: Tue Nov 11, 2014 1:32 am

RS232 Hardware Flow Control in Windows 7

Post by jkeogh »

I am using my Fit-PC3's serial port to control a device which uses hardware flow control. I'm also using the Python serial library to do so.
When I boot into Linux, the flow control works as expected.
When I boot into Windows 7 the same code does not work.

I have found I get an appropriate response from my device if I unplug and reconnect it, but only one response until I unplug/re-plug again.

I the Device Manager I have set the serial port to use Hardware Flow Control.

Is there some setting that is stopping RTS/CTS from working in Windows 7?

Regards,
John

Further to this I have done some testing on various PCs.
I dug out my old RS-232 Level Tester and found the following quiescent states:
HP Desktop PC - Windows 7: TX, RTS, DTR all Inactive (-ve)
Fit-PC2 - Windows 7: TX, RTS, DTR all Inactive (-ve)
Fit-PC2 - Linux : TX, RTS, DTR all Inactive (-ve)
Fitlet - Linux : TX, RTS, DTR all Inactive (-ve)
Fit-PC3 - Linux : TX, RTS, DTR all Inactive (-ve)
Fit-PC3 - Windows 7: TX, RTS, DTR all Asserted (+ve)

So far my research turns up that all lines (TX, RTS & DTR) should be Inactive (-ve) in the quiescent state (before and after transmissions).

The last one is odd: Fit-PC3 with Windows7.
I'm tending to think that there is a driver issue or setting that is causing the incorrect levels.
There doesn't appear to be any driver updates for the serial port on the Fit-PC website.
So can anyone tell me what setting I need to make or driver to update to fix this?
Thanks,
John

mbirger

Re: RS232 Hardware Flow Control in Windows 7

Post by mbirger »

There is no special driver for serial comms on fit-PC3 and it is part of System driver.
http://fit-pc.com/wiki/index.php/Fit-PC ... _Windows_7

What exact behavior does it lead to?
The easiest way to reset any wrong setting in BIOS is simply to reset it:
http://fit-pc.com/wiki/index.php/Fit-PC ... leshooting

Our Windows expert will take a look at this as well.

jkeogh
Posts: 7
Joined: Tue Nov 11, 2014 1:32 am

Re: RS232 Hardware Flow Control in Windows 7

Post by jkeogh »

The behavior it leads to is this:
I have a Data-logger that uses the serial port.
When the port is opened the data logger sends an identification string.
I use this to confirm it is ready to receive commands.
But as the DTR/RTS are asserted on startup that identification string is immediately sent and not when I connect.
I can get around this by dropping the control lines and then re-asserting them, but it shouldn't be necessary.

It isn't the case in other Fit-PCs I have, nor this one in Linux.
I had thought it was a hardware fault, but the control lines are initially inactive when running Linux, hence I suspect some setting in Windows.

I have only one Fit-PC3 so I can't check another.
Can you tell me if Fit-PC3s running Windows 7 assert the serial control lines under normal conditions?

I did update the BIOS and drivers from your website, but have not reset the BIOS so I'll give that a go.
Thanks for the advice.

mbirger

Re: RS232 Hardware Flow Control in Windows 7

Post by mbirger »

BIOS update also reset it.
I have forwarded the question to relevant guys.

jkeogh
Posts: 7
Joined: Tue Nov 11, 2014 1:32 am

Re: RS232 Hardware Flow Control in Windows 7

Post by jkeogh »

Has there been any response from "the relevant guys"?
It's been a while now.

mbirger

Re: RS232 Hardware Flow Control in Windows 7

Post by mbirger »

You are right. Checking.

Leonid
Posts: 157
Joined: Sun Apr 26, 2009 5:10 pm

Re: RS232 Hardware Flow Control in Windows 7

Post by Leonid »

Hello,

I apologize for delay.

Unfortunately, we have very limited COM settings control in the Device Manager. In the future, we can try to find another solution for this problem, but can not commit for the specific date.

fitlet and fit-PC3 have the same SuperIO chip, but the fit-PC2 has another SuperIO chip.
Can you, please, check the same scenario on the fitlet with Windows?
Leonid Firdman

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