Why use true logic in the RFID card reader?

william chan

All PCs use inverted logic.
So if the serial RFID card reader uses inverted logic instead of true logic, we would be able to connect it directly to a PC with just a couple of resistors.
What's the logic behind using true logic?

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Ken Gracey

William,

If you want to connect the Serial RFID Reader to a PC, see this:

http://forums.parallax.com/forums/default.aspx?f=21&m=180521

If you're asking a design question it probably will not be answered, as the engineer doesn't frequent these forums.

Ken Gracey
Parallax, Inc.

Chris Savage

PCs don’t use inverted logic…the serial port simply uses inverted baud mode as a result of the RS-232 drivers, which inherently invert the signal. Of course, it is typically inverted again on the other side resulting in a once again, true (non-inverted) signal. Microcontrollers typically work with these signals, and if you open an external modem up you’ll see they also have inverting drivers to convert back to the non-inverted signal. I have a Hayes compatible at home with 1488 and 1489 line drivers in it. The computer it came off from (80286) had the same drivers on this inside. Take care.

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Chris Savage
Parallax Engineering