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boardnewbie
05-15-2006, 05:37 PM
I just got RFID module (http://www.parallax.com/detail.asp?product_id=28140) and i connect VCC to USB as power source , SOUT to serial pin 2 , GND and /ENABLE to ground of USB port.. and i try to use it in hyper terminal try both com1 and 2 but not seem to work...
anyone out there could help PLZ..

Thank a lot
newbie

Jon Williams
05-15-2006, 07:36 PM
It's not likely your USB port is assigned to COM1 or COM2, and even it it was, the data coming out of the RFID is probably not the correct polarity -- you may have to invert it.

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Jon Williams
Applications Engineer, Parallax

Bruce Bates
05-15-2006, 07:49 PM
Jon -

Above and beyond that, if I understand correctly what "boardnewbie" is trying to do, the USB port doesn't have sufficient, or barely sufficient power to drive the RFID unit, does it?

Regards,

Bruce Bates

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Jon Williams
05-15-2006, 08:08 PM
I don't know -- I've heard USB ports can supply 500 mA; is that wrong? I wouldn't attempt to drive it from the USB supply, but that's just me.

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Jon Williams
Applications Engineer, Parallax

Chris Savage
05-15-2006, 11:04 PM
Initial power-up current of the USB Port is limited to 100mA. Once the USB controller is enumerated the current limit is raised to 500mA. As far as I know the device must request to be recognized as a high-power device for this to happen. Usually the device will control switching of the power if it is a high-power device so that when the device has been recognized as high-power it switches on the connected equipment via a MOSFET. If I am reading the FTDI sheet correctly by default they do not support anything over 100mA on the bus. You must write a register in the EEPROM of the chip (FT232R) to sepcify up to 500mA of current draw.

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Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)