A while ago I posted a message asking for suggestions to solve a problem
I was having in getting XP to load software into an embedded device I had
worked on. Win98 worked fine. The priorities changed for a bit and
wasn't able to get back to it until recently. Since there were many
helpful responses I owe the solution back to the group. XP will transmit
serial data freely, but will not receive data unless DSR is set. Win98
doesn't seem to care.

Thanks again,

bosch

On Fri, 07 Nov 2003 16:41:00 -0500, Mickey wrote:

I am using Delphi. In your case, was the comm bi-directional?

-bosch

That cannot be true because I transmited data from one COM port to
another COM port and I only had Rx, Tx and GND lines connected to the
ports and it worked as expected. That was all done on Windows XP, by
using pure Win32 in Visual Studio 6.

BTW, what program (VB, VC++, Delphi) are you programming in for Windows?

Jonathan Bosch wrote:
there seems to be a problem,
but it's depending on the OS, the hardware and the wheather ;-)
Although is from a specific commport component, I've seen similar
effects with other drivers.

Many users reported a problem : when there isn't any device connected to
the COM port, the ReadFile/WriteFile APIs hang the system (or at least
slow down it). It seems that the Win32 kernel always waits for the DSR
line to be set.
To prevent hangs, set CheckLineStatus to TRUE before calling Connect.
When CheckLineStatus is TRUE, the TCommPortDriver component never calls
ReadFile/WriteFile APIs if none of the following are true:

for ReadFile :
1. at least one must be set (CTS, DSR, RING, RLSD)
2. or: (RX queue is not empty)

for WriteFile:
1. at least one must be set (CTS, DSR, RING, RLSD)
2. and (TX queue is not full)

Checking the state of CTS, DSR, RING and RLSD signal doesn't work if you
are using a three wire cable (RX, TX and GND).

Stef Mientki

Mickey wrote:

.... isn't that from M$ ?
Well they have the advantage of knowing where the bugs are,
and so they can write an (invisible) wrapper around it.
Stef Mientki

Jonathan Bosch <newton@easystreet.com> wrote in message news:<vqnml73b8h9vea@corp.supernews.com>...

Make sure you're specifying "No DSR Sensitivity" for the device with
SetCommState() (DCB.fDsrSensitivity = FALSE) just after the
CreateFile().

The ports were bidirectional, and I'm pretty sure that your problem
is caused by Component you are using, because when I used pure
Win32 programming with standard Win APIs (Win XP) I had no
problems reported by other (when no device is connected or so ...).

Others have written about those components so I hope that helps you.


Best regards, Mickey.

Jonathan Bosch <newton@easystreet.com> wrote in
news:vqobuietloqkfd@corp.supernews.com:

If you are doing it in straight WinAPI, make sure to do the following:

const dcb_Binary = $00000001;
var dcb: TDCB;

fillchar( dcb, sizeof(dcb), 0 );
// Setup dcb (Device Control Block) fields
dcb.DCBLength := sizeof(dcb); // dcb structure size
// set baud, etc...
// code snipped

Handle := CreateFile(Port,
GENERIC_READ or GENERIC_WRITE,
0, // Not shared
nil, // No security attributes
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
0 // No template
) ;

If Handle <> $FFFFFFFF then
Begin
// Set fBinary: Win32 does not support non binary mode transfers
// (also disable EOF check)
dcb.Flags := dcb_Binary OR DTR_CONTROL_DISABLE OR
RTS_CONTROL_DISABLE;
SetCommState( Handle, dcb );
// code snipped...

The dcb.Flags and SetCommState are the important bits. I set all dcb
properties directly. You could also use GetCommState and just modify
the ones you want to change.

HTH.
Jeff.