| Author | beginning argument ( Replies received: 2 ) |
| russ1 |
 Posted 19-06-2008 at 17:36 |
Registered on :
06-10-2008
Messages : 33
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I only have one usb port on the device I am designing and I really need RS232 to come out on it along with USB. I'm trying to figure out a way to allow this either by muxing or selectively enabling/disabling the MAX232 chip. The data is going out over a USB cable. Anyone have experience with this?
This is the closest mux I could find, but it doesn't have have a low enough negative voltage throughput to allow the RS232 signal:
http://www.intersil.com/data/fn/FN6515.pdf
Is it possible run USB lines through a FET (note: I only need low-speed USB)
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| STOne-32 |
 Posted 19-06-2008 at 22:08 |
Registered on :
05-29-2007
From STMicroelectronics
Messages : 315
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Hi russ1,
Be carefull STR7 USB are only Full Speed and Not low-speed.
ST1.
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| volius |
Posted 20-06-2008 at 06:28 |
Registered on :
09-12-2006
From UK (United Kingdom)
Messages : 131
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It's not easy to find an analog multiplexer that would accomodate the range of RS-232 and have sufficiently low ON-resistance. Have a look at this one:
www.analog.com/en/prod/0,,768_836_ADG608%2C00.html
It has ON-resistance of 22 Ohms, which might be good for USB, and voltage range of +/- 5 V. If you limit the voltage range of RS-232 to +/- 5 V, you could get away with this mux. And you must hope that +/- 5 V is enough for the RS-232 receiver on the other end (it should be fine, though.)
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USB and RS232 line sharing with a mux