mfc, USB-to-serial converter problem

microsoft.public.vc.mfc - Microsoft Visual C


mfc >> USB-to-serial converter problem

by Mike Shride » Thu, 27 Nov 2003 02:45:25 GMT

I have a program that receives up to 200K of serial data. To do this I
enabled "automatic" hardware handshaking by setting DCB.fRtsControl =
RTS_CONTROL_HANDSHAKE and DCB.fOutcCtsFlow = TRUE. When DCB.fRtsControl is
set, the serial port driver automatically raises the RTS signal to show that
my program is ready to receive data.

This works correctly with a normal serial port. However, when I try to use
my new USB-to-serial converter (IOGEAR GUC232A) the RTS signal is _not_
raised by the USB driver and consequently the external device thinks that my
program is not ready to receive data.

Is this normal behavior for USB-to-serial drivers? Does anyone know of a
USB-to-serial converter that behaves exactly the same as a normal serial
port?

BTW, I have the same results whether I use RTS/CTS or DTR/DSR handshaking.

Thanks,
Mike




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mfc >> USB-to-serial converter problem

by Matt Claessen » Thu, 27 Nov 2003 05:19:04 GMT


Hi,



I have used a Keyspan 4 port USB to serial converter (USA-49WLC).
It supported all hardware handshaking lines in the serial interface.
Our application really needed these lines, because it used them to
control some device.
I could not get confirmation from Keyspan before buying, so I
took the chance of wasting the money.
It worked perfectly, however.
Another example of a product being much better than its sales
or support.

regards, Matt




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mfc >> USB-to-serial converter problem

by Mike Shride » Thu, 27 Nov 2003 07:12:16 GMT

Matt,

Most all USB-to-serial converters claim to support hardware handshaking.
But there is a big difference between supporting "automatic" serial
handshaking versus "software" serial handshaking. I need a converter that
supports "automatic" handshaking.

Thanks,
Mike




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USB-to-serial converter problem

by Matt Claessen » Thu, 27 Nov 2003 18:15:51 GMT

Mike,

Can't you just toggle the line yourself then, with EscapeCommFunction ?
Since these devices are primarily targeted at Mac users besides Windows
users, I think you will have a very hard time getting the exact capabilities
from the sales people.
You expect not only hardware compatibility, but also exact Windows driver
emulation. That seems like a tall order.
I could not even get these people to confirm any hardware line
compatibility, they probably didn't know what I was talking about. Their
device was RS-232 compliant and that was it!

regards, Matt



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USB-to-serial converter problem

by Mike Shride » Thu, 27 Nov 2003 23:41:11 GMT

Matt,


I could - but I'd have to rewrite my worker thread to detect when the input
buffer starts to fill up, or empty out, and that sounds like a lot of extra
work to me. And to be honest I haven't looked at any code that manually
toggles the line to control handshaking. I just figured it would be easier
to ask the question first.

Actually, that brings up another point. I wonder if there is any way to
determine if a COM port is a "real" COM port or a USB emulated COM port.

Mike





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USB-to-serial converter problem

by Matt Claessen » Fri, 28 Nov 2003 03:46:08 GMT

Hi,,



That's a tough one.
Depends on how good the emulation is.
The ports are enumerated in HKLM\hardware\devicemap\serialcomm
However, that included the virtual ports in my setup.
You could check whether the virtual ports are also included in e.g.
HKLM\hardware\description\system\multifunctionadapter\5\serialcontroller\0
where 5 stands for ISA in my machine.
Chances are that only the real ports are listed under ISA.

Sorry I can't be of more help, I don't have the Keyspan device anymore.

Good luck!

regards, Matt



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I have a program that receives up to 200K of serial data.  To do this I
enabled "automatic" hardware handshaking by setting DCB.fRtsControl =
RTS_CONTROL_HANDSHAKE and DCB.fOutcCtsFlow = TRUE.  When DCB.fRtsControl is
set, the serial port driver automatically raises the RTS signal to show that
my program is ready to receive data.

This works correctly with a normal serial port.  However, when I try to use
my new USB-to-serial converter (IOGEAR GUC232A) the RTS signal is _not_
raised by the USB driver and consequently the external device thinks that my
program is not ready to receive data.

Is this normal behavior for USB-to-serial drivers?  Does anyone know of a
USB-to-serial converter that behaves exactly the same as a normal serial
port?

BTW, I have the same results whether I use RTS/CTS or DTR/DSR handshaking.

Thanks,
Mike

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Yes, some of us, like me, still need Serial ports!!! Drives me nuts
that it is almost impossible to still get a high end motherboard these
days that has a built in serial port...

I just found out yesterday though, using my serial boot loader for my
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For this bootloader, I can live with it and things are working.

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Using the System.IO.Ports.SerialPort class to do this...

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kimi no koto omoidasu hi nante nai no wa
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