Serial COM port help

[DMA02]

Hi, I've got a really weird problem with a serail com port device.

First off I know that the actual device, 20 col line display for point of sale machines, is working. I have 2 windows XP machines, one has 1 serial port the other has 4.

1. I plug the serial device into Machine 1, and immediately the device screen shows some version info showing that it works.
2. I plug the serial device into Machine 2, and nothing happens.

I run the following DOS commands on both machines

mode com1:96,n,8,1
echo test>com1

1. On machine 1, the text "test" is displayed on the device
2. On machine 2, nothing is displayed.

I check the device settings in System->Device manager->Com1 on both machines and made sure they're both exactly the same, and still doesn't work.

I'm completely stumped. I have a printer that connects to the serial port that works on both machines, but my line display device only works on 1 of them.

Does anyone have any idea why or some config that I may have overlooked ?
Thanks.

[Geek-9pm]

Trying to test serial devices without the proper tools is a real pain.
Standards for the RS-232 interface have be altered over the years.
In addition to that, how a device responds can be unprofitable if the handshake lines and not used properly.

I am not joking with you. I used to work as a advanced technician many years ago. Serial ports were horrible back then. It is supposed to be better now!
If you do not want to spend a lot of time on this, you can get a gadget that resolves serial interface problems with older equipment.

But wait. If all the stuff is new, get back to your supplier and throw the problem on him. New equipment should not do this at all.

Try your device on as many PCs as you can. If you get mixed results, the cable is not wired properly for the device. Or the device does not conform to current standards.

Here is a tutorial.
http://www.arcelect.com/rs232.htm

I hope this is of some help. Let us know which direction you go with this.

EDIT: A quick fix maybe to just use a USB to RS232 adapter.

[JJ 3000]

Are you using the same data cable with each of the computers?

[DMA02]

Yes the data cable is the same.
Also want to say that the behaviour is consistent.

Machine 1 works.
Machine 2 doesn't work.

Though I know that Machine 2 has more windows service packs and updates installed, don't know if this makes a difference. But it works on one and not the other.

[DMA02]

EDIT: A quick fix maybe to just use a USB to RS232 adapter.

Man, I actually was at radio-shack yesterday looking for one and they didn't have any

[JJ 3000]

Have you checked BIOS to make sure that the serial port is enabled?

Is it the machine with four serial ports that is not working?

By the way-
You can get those adapters online.

[DMA02]

The machine with the 4 serial ports works.
The one with 1 serial port does not.

I also want to make it clear that the serial port on on the machine with 1, works because I tested a printer on it. When I hook up my Line Display device it doesn't. The line display device only seems to work on my second machine (the one with 4 ports only)

[DMA02]

Checked the BIOS settings of both machines.
1 thing I saw on the one that worked is all the com ports have a "PWR enable/disable" setting along with another setting to enable or disable the com port.

Can this mean that the device draws electricity form the com port to actually function ? If this is so.. it could be the problem.

http://www.tkk.fi/Misc/Electronics/circuits/rspower.html

[Geek-9pm]

The machine with the 4 serial ports works.
The one with 1 serial port does not.
I also want to make it clear that the serial port on on the machine with 1, works because I tested a printer on it. When I hook up my Line Display device it doesn't. The line display device only seems to work on my second machine (the one with 4 ports only)

Try the device on two more machines.
Call a friend. Borrow a Laptop.

[DMA02]

The power-mappings are different on each machine.

[DMA02]

After some searching around several documents, it turns out that the serial device I have needs a COM port that supports +5V power on the serial port. Something provided by the BIOS.