Re: RS232 ports and new PC's

I had the same experience : no significant issue using a USB to RS232 cable, as long as :

- the software is able to use exotic COM ports (usually recognized as COM3 or even COM5 on my PC, depending on the USB connector used...)

- the peripheral don't try to grab current from the RS232 port. I had some issues with a programmer that tried to get -12V from it... But it is similar with issues found on laptops RS232 ports.

Cheers,

Robert Lacoste - ALCIOM : The mixed signals experts

"Mark A. Odell" a écrit dans le message de news: Xns93C8AD88D7539lkj562ghjgk1k245lbvj@130.133.1.4...

"CM" wrote in news:CSTVa.13267$R14.9760@news- binary.blueyonder.co.uk:

Have used them, but not with DOS apps, so can't say for certain.

OK on a desktop, not much use on a laptop...

Agreed, but you could use a pcmcia rs232 card, It wouldn't look plain vanilla from a hardware point of view but perhaps still cleaner than usb.

My laptops are old (P133) and have serial ports, but I guess a lot of the latest kit doesn't...

Chris

Colin,

The command prompt in Windows machine is not the same as a DOS environment. Also, a console app is not the same as a DOS app.

USB based adaptors will not work with DOS apps. It is impossible. If you want to use your old DOS apps, then you have to use either PCMCIA, PCI or ISA.

Elroy

Quatech do PCMCIA serial and parallel IO cards that look like "native" ports from a SW point of view. I use the parallel port one in my laptop for programming FPGAs.

My boss likes to joke about "the world's most expensive parallel port" - it cost us about AUD$300 (approx US$200).... which is a shocking amount of money for essentially a bit of cable, a latch and a PCMCIA controller, but anyway, it works perfectly, even with legacy bit-banging software.

John

Colin, I have not used USB to RS-232 because sometimes there is a problem according to some vendors. I believe it has to do with latency, but I don't recall exactly. I have used TCP/IP to serial and they seem to work fine. Check with Digi, Equinox, and Moxa (in no particular order). Of course this means your laptop will need a network port.

Dennis,

DOH! We are not talking about writing a Windows driver, we are talking about accessing USB hardware on a machine that is running DOS. It is quite impossible. DOS doesn't even know what USB is! DOS has no USB stack! DOS has no idea how to work with USB hardware.

We make these serial adapters here at work. We know these things...

Elroy

perfectly

register

I was merely commenting on the "impossible" statement. DOS does not know about USB, so doesn't windows without the appropriate drivers. You should know these things...... Do a google search on "DOS" and "USB". you'll find software solutions that make USB work in DOS.

Meindert

The OP stated in part, " will some of my old DOS apps be able to access one of these ports when running from the command prompt of Win2K or XP Pro ?"

So he/she was not talking about running stand alone DOS, but the dos emulator (under Win XP) for example. - RM

perfectly

register

Have a look at

Sure you can. I have used public domain ulilities that capture access to the hardware UART registers. The same mechanism can be used to capture serial data from a DOS app, stuff it into a USB stack and pass it on to a USB-serial converter. If you create a Virtual Machine, a DOS application has no knowledge whether it is talking to real hardwar or to a I/O port in a vitual machine.

Meindert

and than there is one mfr. that has one only header for a commport on the motherboard and it does not work. I have to "remove" the commport from the systems setting and restart the computer before the commport is active. Even got a new bios upgrade from the mfr., no help rw

Do a google for USB and DOS. There are quite a few drivers available for Mass Media type devices.

Regards Anton Erasmus

"Meindert Sprang" wrote in news:3f37add8$ snipped-for-privacy@news.nb.nu:

Doesn't that depend on the application though? I would have thought that well-behaved proggies would use standard OS calls wheras naughty proggies would access hardware directly, without notifying the OS. The former would run in a virtual machine no problem but I'm not sure about the latter case; surely the proggy would just attempt to look for non- existant hardware? I've certainly come accross progs that wouldn't access COM ports at non-standard addresses (or even anything else other than COM1 and COM2) so they were definitely looking directly at hardware.

We have development system that requires an RS232 port with a working DTR, and preferably a working DSR. We tried several RS232/USB converters and found one that worked well on all Windows OSes across different versions and configurations of our systems so we resell it on our Webstore.

Some customers have tried OTS serial port cards and found that the DTR didn't work.

RS232 ports are going away faster on laptops, and the quality of the ports and drivers can be questionable. A major laptop/desk maker had the DTR glitching when the port was closed and reopened. They posted a patch, but we had to patch our SW to work around the problem too.

-Brian

Most DOS comm programs I know access the ports directly. At address 0:400 you can find a list of addresses (maximum of 4) of com ports found by the BIOS during power-up. In a virtual machine, an I/O access from an application results in an exeption interrupt, which in turn is handled by the OS (add-on). The interrupt handler will in turn transfer the data to/from the I/O port address and returns eventually. The application knows nothing about this and continues as if a normal I/O access has taken place. A google search on "I/O privilege map" will turn up several links describing this.

Meindert

"Meindert Sprang" wrote in news:3f380997$ snipped-for-privacy@news.nb.nu:

Thanks!

Correct, and my orig "No. Under Win2K or XP, your old DOS app will not be able to access one of these ports when running from the command line prompt."

Elroy