Are USB to Serial cables created equally?!

[newbie_atit]

Looking for help!

I have been attempting, unsuccessfully to this date, to connect a numeric keypad to the USB port of a Dell notebook (operating under WindowsXP-home) for quite some time, using a USB serial cable.

I know for a fact that the keypad is in fine working condition as I have been able to use it when connected it to the serial port of Dell notebook (operating under Windows98SE) or to the serial port of a desktop PC (operating under WindowsXP-Pro).

The reason for the title of this post is that I have been able to use the keypad when connected to the Dell notebook (operating under WindowsXP-home) with a friend's USB serial cable. The difference between my friend's cable and mine is one of price, namely is is about 3 times more expensive than mine. So, although the cable looks the same, is it possible that the wiring at the serial connector end is different?

When my cable (cheaper one) is first connected to the USB port, WindowsXP installs the necessary drivers and Device Manager reports it initially as a Human Interface Device (HID). Then, when the driver of that device is updated with the installation CD provided with the cable, once the installation is finished, the device gets now reported under Ports (COM & LPT) as a USB-HID->COM device and is said under Properties to be working properly and with the following 2 drivers (HidCom.sys and serenum.sys) installed in C:\Windows\system32\drivers. disappointingly, the keypad does not work when connected (same COM port on both devices) to the serial connector of the cable.

Any assistance on how to resolve this "challenge" will be greatly appreciated.

Newbie_atit

[slgrieb]

Just to be sure I'm clear on this, I think you're saying the keypad works on your computer with your friend's cable. If that's right, you have answered your own question. Not all cables are created equal. You could have a defective cable (short, broken wire, etc) but most likely you just have a cable that doesn't meet the standard for USB cables, no matter what the manufacturer claims.

[newbie_atit]

Thanks for your comments, slgrieb.

I do have a suspicion that all USB-serial cables are not identical in terms of their wiring! The idea behind my post is to establish whether somebody else has experienced the same situation.

[Froghead]

I've sold dozens of USB/serial adapters mostly to boaters for use with a GPS.
Sold probably a half dozen diff brands, usually no name without many problems. Do run into problems with older odd diagnostic equipment that was never meant to port over to USB. So yeah, it could be any one of incompatible (not necessarily cheap) cable, drivers or the keypad.

If you're friends cable works on your machine and your cable works for him just ask kindly to switch cables.

Then again a quick check at www.belkin.com shows a USB/Adapter at $59 and a USB Keypad at just $24.95. Hmmm...

[hey__me]

Being in the industrial world, Not all USB to Serial are the same. The biggest thing I see is that the Voltage and current ablity of the serial ports very. A lot of Serial devices that do not have there own power supply have problems with various adapters. The Old built in serial ports mostly used +/- 12V as there signal levels. Since power was derived straight from the motherboard, most of these had a fair amount of current available as well. With the USB devices, only 5V is available on the USB port. Current is also strictly regulated for self powered devices. The device has to ask for a certain amount of power from the bus. Because of this, most manufacturers try to make there USB devices as low power as possible so the bus controller doesn't complain and they get enough juice. Very often you will see that the Voltage levels are only +/- 5V and there isn't enough power to run any electronics attached to the serial lines.
The Belkin PDA serial adapter seems to be pretty good, The Startech one works with most things, but I have ran across stuff that will work with one but not the other and vice versa.

So good luck, and if you find what works with your serial device, stick with it.

The other problem is with software. A lot of older Dos/Win95 software was written to directly access the UART on the serial port. Since the UART now resides on the USB bus on not as a physical Port on the I/O Bus of the CPU, there exists some software that will not work with any USB or PCMCIA Serial Ports.

[Grateful_Dad]

Just to add my .02
The cable isreally an electronic circuit - not a pin to pin converter. The serial end ( usually - since its' bigger ) has an actual IC chip to convert from USB to Serial. That is why they are not all created equal. Some converter chips are better than others - as you have seen with your friends cable.
I just wanted to point out that it is not a pin-to-pin adapter.
HTH

[slgrieb]

Absolutely right about converter chips, but I have had some off-brand cables that didn't meet USB 1.1 specs. Cable specs for USB 2.0 are identical to USB 1.1. So if you use even a USB 1.1 cable to connect a 2.0 device to a 2.0 port, you should get a high speed connection. If you don't, then you have a cable that doesn't meet the USB 1.1 spec. Proving once more that anything can be made cheaper and sleazier, no matter how trivial the savings.