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From: D Yuniskis on 10 Apr 2010 02:30
eeboy wrote:
> I need an IC to share a UART between two devices. The TX/RX voltage will
> range between 3.3V and 5V. The data rate is 115,200 bps. I've found a few
> IC's capable of handling this but they are all so expensive (ex: MAX399 @
> $2.70 in qty 2500). Any other suggestions?

Huh? You aren't planning on switching the signals *on*
the EIA232 interface, are you? I.e., I assume you have one
UART that wants to talk to two different "external"
devices.

If so, install your EIA232 level translators connected to the
pins of the "external connectors" (i.e. DB9's or DB25's).
Now, you have all "logic level" signals to play with
(3V or 5V depending on the translators you chose).

Put a (logically, OR) gate in series with each output (Tx)
signal (before getting to the level translator. Drive a
signal to the other input of each gate -- use that signal
for one of the gates and the complement of that signal
for the other (this can be one signal passing through an
inverter -- or, two signals that you deliberately drive
in complementary fashion from the processor).

Whichever external device is NOT in use has this "control
input" driven HIGH. This forces the EIA232 driver to
emit a marking condition regardless of the state of the
actual Tx signal from the *real* UART.

Meanwhile, use a 2-to-1 mux to combine the Rx signals
from the translators into a genuine Rx signal fed to
the UART. Drive the "select" input with the same
control signal used for the Tx circuitry. This causes
the input from one of the Rx paths to be ignored in favor
of the other.

By careful choice of gates, you can probably fabricate the
mux out of spare gates left over from the gating of the
Tx signal(s).

Or, have I totally misunderstood your question? <:-(
From: TTman on 10 Apr 2010 02:26

"eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in message
news:O8Cdnfmj74EZTyLWnZ2dnUVZ_tednZ2d(a)giganews.com...
>I need an IC to share a UART between two devices. The TX/RX voltage will
> range between 3.3V and 5V. The data rate is 115,200 bps. I've found a few
> IC's capable of handling this but they are all so expensive (ex: MAX399 @
> $2.70 in qty 2500). Any other suggestions?
>
>
HC4053 with diode clamps/resistors to get 5V tolerance....gives you 3 lines
of mux.


From: Nico Coesel on 10 Apr 2010 03:16
"eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote:

>I need an IC to share a UART between two devices. The TX/RX voltage will
>range between 3.3V and 5V. The data rate is 115,200 bps. I've found a few
>IC's capable of handling this but they are all so expensive (ex: MAX399 @
>$2.70 in qty 2500). Any other suggestions?

74HC4051

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico(a)nctdevpuntnl (punt=.)
--------------------------------------------------------------
From: Jan Panteltje on 10 Apr 2010 07:46
On a sunny day (Fri, 09 Apr 2010 20:21:08 -0500) it happened "eeboy"
<jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in
<O8Cdnfmj74EZTyLWnZ2dnUVZ_tednZ2d(a)giganews.com>:

>I need an IC to share a UART between two devices. The TX/RX voltage willrange between 3.3V and 5V. The data rate is 115,200 bps.
>I've found a fewIC's capable of handling this but they are all so expensive (ex: MAX399 @$2.70 in qty 2500). Any other
>suggestions?

PIC

LOL
And that can probably replace your devices too.
From: David Eather on 10 Apr 2010 13:01
On 10/04/2010 11:21 AM, eeboy wrote:
> I need an IC to share a UART between two devices. The TX/RX voltage will
> range between 3.3V and 5V. The data rate is 115,200 bps. I've found a few
> IC's capable of handling this but they are all so expensive (ex: MAX399 @
> $2.70 in qty 2500). Any other suggestions?
>
>
>
> ---------------------------------------
> Posted through http://www.Electronics-Related.com

PIC. (no LOL)
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