USB and serial cable connection(s)

[ardhuru]

Hi, I am designing a board on which I have a serial and a USB connection to be connected to a PC. Since its a minimal serial connection, I am thinking of combining the USB and the serial signals on just one 9 pin D connector at the board end. At the PC end , the cable would be split up into a separate serial and the USB connectors. The idea here is to have just one cable running between the PC and the board.

Now, I've noticed that the USB plugs are designed such that the power pins always make contact before the data pins do. With my design, that might not happen at the board end. Is this likely to damage the USB port on the PC? Or at the least would the PC have problems recognising the board at times?

Is this a bad idea, and should I just have two separate cables?

Regards,

Anand

[BrianT]

*******ised cables & connectors will almost surely bite you eventually. They certainly have for me. You are making a 'proprietary' interface. I say stick with the industry accepted connectors and pinout and you will not be going beserk trying to find the schematic with the pin out in 3 years time.

HTH
BrianT

[dhouston]

Before deciding you should read the USB spec to see why the plugs are as they are.

• http://www.usb.org/developers/docs/

[ardhuru]

Right, Brian, Dave. Point noted.

Regards,

Anand