There seems to be two different types of com ports on laptops. A
notebook that has a phone modem seems to have a partial com port. Two
laptops with modems can't communicate through the serial ports but if
one doesn't have a modem they can communicate. Just what is the
difference between a laptop with modem and one without as it relates
to the serial port?


thx

external modems use serial port connection
"Worf son of Maugg" <Me@KnowWhere.org> wrote in message
news:u4rsk1h0hrrb349oml4fg1bm6nessct2oq@4ax.com...

Worf son of Maugg wrote:
The modem uses a COM port that is shared with another on-board COM port.
COM1 is shared with COM3; COM2 is shared with COM4. So on a computer
with an internal modem, check the modem properties and if it is COM1 or
COM3 that is used, select COM2 or COM4 for serial communications. If
the modem is using COM2 or COM4, then use COM1 or COM3 for serial
communications.

Q

On Thu, 13 Oct 2005 16:37:59 -0600, "Quaoar" <quaoar@tenthplanet.net>
wrote:


I understand the relationship between com1,3 and com2,4 as it relates
to interrupts and memory addresses. My question has to do with the
implications on an embedded modem in a notebook. It seems like the
pinouts TD (Transmit Data), RTS (Request To Send) and DTR (Data Set
Ready) are routed away from the com port and connected to the modem.
You can test this theory by using a RS232 tester and comparing two
ports one from the desktop PC and the notebook. If true can this be
changed so the com port has all the capabilities that a desktop PC com
ports has.

I never heard of a serial port on a laptop lacking flow control. There
is no reason for it to do so. The internal modem uses CMOS signal
levels, so it's not like they need to steal the RS232 driver/receiver
pairs for the modem. And each UART has its own separate flow control
lines. Check the datasheet for any super I/O chip.

zwsdotcom@gmail.com wrote:
I suspect that the OP needs to determine the exact chipset on the
laptops in question and then determine if the I/O chip that handles
the serial port and modem port has some restrictions on operation.
It's entirely likely, for instance, that a single serial port is some
how virtualized between the two ports, and that they don't both play
together together. Or maybe there's only one set of hardware
handshake lines, and they are used for modem control, and unavailable
for serial port use. The solution could be as simple as the latest
chipset drivers or as 'complex' as "don't do that".

Why bother trying to communicate between laptops using serial ports
these days anyway? Network or USB or WiFi is going to be a lot easier
to implement, and a lot faster besides...

On 14 Oct 2005 10:20:47 -0700, zwsdotcom@gmail.com wrote:


Thanks for the reply!

I got a IBM think pad and when I connect my comm. "mini-tester" (like
this one "http://www.scancat.com/minitstr.html") to it I don't get any
indication until I hit connect button on the term program
But when I connect it to a standard PC's 9-pin serial port I get
indication on TD (Transmit Data), RTS (Request To Send) and DTR (Data
Set Ready) without the term program even running. I use it communicate
with CNC machines to up/down load text files they for programs.
Desktop PCs or notebooks (w/o modems) work with the machines but at
least two notebooks the ThinkPad and an old 80286 notebook (both with
modems) do not work. The light on the tester twinkles like data is
flowing but nothing shows up in the term. Both notebooks work with
desktop PCs but not with each other or with the CNC machines. This
leads me to think that there are two types on comm. ports in this
world "dumb" and "smart". Dumb on the CNC machines and notebooks with
modem and smart as in desktop PCs. Thus two dumb comm. ports can't
talk to each other and that there must be at least one smart port
involved to work.

William P. N. Smith <> wrote in news:tfuvk190f2353ql758sfvdkt4rfr0s0mks@
4ax.com:

There is, unfortunately, a large minority of us out here in the real world
of communications service, network IT and radio communications, that need
'real' RS-232 serial ports with all the control lines. Many routers and
other control devices in 'legacy' networking environments and radios(both
base station and mobile) can only be set up or tested using rs-232 ports.
It's one thing to talk about a $1000.00 laptop with or without serial
ports, it's another thing to talk about several millions of dollars of
infrastructure that still needs them.

We have also run into the problem that on some brands of laptops the
'serial ports' were not true rs-232 compliant ports. They would not operate
our RIB's (Radio Interface Box) which we used to do field programming and
troubleshooting on Motorola radios in trucks, often hundreds of miles away
from our shop desktops. At one time we went so far as to pack up one of the
laptops and a complete mobile radio system and sent it to a Motorola
software lab. They finally sent the setup back with a shrug. Besides
confirming that model (DEC) laptop could not be made to work, they found
that half the IBM brand models their people owned also would not work.

Then there's the issue of trying to run some of those old (DOS based)
programs on the current CPU speeds. But that's another story....

Lee


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Forget about this tester. Put an oscilloscope on the port and see what
the actual signal levels are.

Perhaps this may solve your problem:

http://www.neteon.net/prod.asp?pc=56...rial%20Adapter

http://www.neteon.net/cat.asp?c=43



"Worf son of Maugg" <Me@KnowWhere.org> wrote in message
news:u4rsk1h0hrrb349oml4fg1bm6nessct2oq@4ax.com...

On Thu, 13 Oct 2005 14:34:07 GMT, Worf son of Maugg <Me@KnowWhere.org>
wrote:


Well I got a Panasonic Tough Book and it has a half assed comm port in
that rs232 is only partially supported and tech support seems to think
that it works just fine. So if you need full rs232 support the Tough
book is not going to work. Anyone know of a notebook that has a REAL
comm port?

On Thu, 13 Oct 2005 14:34:07 GMT, Worf son of Maugg <Me@KnowWhere.org>
wrote:


Well I got a Panasonic Tough Book and it has a half assed comm port in
that rs232 is only partially supported and tech support seems to think
that it works just fine. So if you need full rs232 support the Tough
book is not going to work. Anyone know of a notebook that has a REAL
comm port?