SparkFun Forums

[brainwav]

Hi is it possible to use my laptops parallel port as a serial port? I was thinking of just (somehow) intercepting the serial communications and send it to the parallel port. Maybe not, but maybe a driver can be written to make the parallel port look like a serial port. Is there already such a thing??

I have a USB-RS232 adapter for my laptop, but it doesn't work on the PLC's we are using. We've tried several of them, so that's why I got the idea to use the parallel port instead.

Is this possible?

Brainwav.

[stevech]

Not all USB-RS232 converters are equal. IMO, the ones that use the FTDI chipset and WIndows driver are reliable. I've had others that were not.

But if your PLC or other relies on very detailed (less than a few mSec) timing of the RS232 RTS/CTS/DCD/DTR then most any media converter will give you problems.

Parallel to serial - years ago you could find them. Not so now.

There are PCMCIA cards for laptops that produce "real" serial ports.

[brainwav]

Parallel to serial - years ago you could find them. Not so now.

There are PCMCIA cards for laptops that produce "real" serial ports.

Would it be possible to make a parallel to serial converter?

When you say "real" serial port, it acts just like a real one? Do you know a good brand of those? How much do they usually go for?

[oPossum]

B & B electronics is my favorite source for industrial communications gadgets. They have several PC Card (PCMCIA) serial interfaces:

http://www.bb-elec.com/product_family.asp?FamilyId=23


The old parallel to serial interfaces that I remember where unidirectional. They allowed a serial printer to be used with a parallel printer port. This would obviously not work for your application.

It is certainly possible to interface a 16C550 UART to a bidirectional parallel port. The hardware would be quite simple. The necessary software support would be the hard part.

[stevech]

Quatech has made PCMCIA to serial cards for years. Pricey.

I assume you have no USB port.

Another option is an ethernet->serial adapter like LANtronix, Moxa and Digi make. Pricey too.

[brainwav]

Does anyone know if the PCMCIA cards work in DOS?? They sound like they are addons to the motherboard.

[silic0re]

Hey Brainwav,

Are you using a DOS console from Windows, or straight DOS? If you're using a DOS environment on a newer laptop (because your PLC programming software is DOS based) and require a serial port, and your USB->serial converter isn't working, then one option is picking up an old laptop with a serial port on it for very cheap -- what may infact be less than purchasing a PCMCIA interface .

I'm sure you could find a 486 notebook on ebay for really cheap.

i hope that helps,
silic0re

[brainwav]

what I am trying to do is use it trhough straight DOS, not a dos box. We have some old hardware that sometimes need maintaining/reprogramming and the only software we have that does it is DOS software. We do have old laptops, but its hard to carry around two laptops; one for all of our other software and one for the old hardware.

If there isn't some DOS serial adapters, is there a way of running dos software in WindowsXp and still be able to use the USB-to-Serial adapters?

[silic0re]

this is kind of off topic, but just normal DOS software should generally run OK in using Windows XP. If you install the USB->Serial device, then in the ideal case (I've never tried it) your DOS software should just be able to access it like any other COM port. You may have to setup which COM port the USB->Serial adapter will be recognized as through the device manager or some other configuration utility.

If you have any problems with running the software itself (such as error messages from XP about running legacy DOS software) then you can always google the errors and I'm sure there are a lot of resources about trying to resolve any incompatabilities. That being said, if it doesn't work out on the newer system, there is always the old laptop idea .

best of luck

[oPossum]

PCMCIA serial cards typically use a 16x50 compatible serial chip that will work with DOS software. You have to run an enabler program to map the I/O and interrupt to standard addresses. Once that is done, the DOS application should work fine.