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From: eeboy on 9 Apr 2010 21:21
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?



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From: a7yvm109gf5d1 on 9 Apr 2010 22:12
On Apr 9, 8:21 pm, "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?
>
> ---------------------------------------        
> Posted throughhttp://www.Electronics-Related.com

How many lines do you have to do the selecting?
What do you mean 3.3 and 5V? Will you need to level translate?
What power supply will you be running the mux at?
From: linnix on 9 Apr 2010 23:20
On Apr 9, 6:21 pm, "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?

Yes, try some standard parts like 4051,2,3. MAX* are usually
expensive custom parts.

From: eeboy on 9 Apr 2010 23:25
>
>How many lines do you have to do the selecting?
>What do you mean 3.3 and 5V? Will you need to level translate?
>What power supply will you be running the mux at?
>

So... a micro and two devices involved. The micro and one of the devices
both run at 3.3V. The other device runs at 5.0V. I currently have the 5.0V
device communicating with the 3.3V micro with no problems. It's 5.0V
tolerant.

The mux will be running at 3.3V so it will have to be 5.0V tolerant... or I
will have to perform some level translation which I'd rather not do
(another component).

I can free up multiple I/O pins to do the selecting but would prefer to
utilize a single I/O pin to select between device A or device B (1=A,
0=B).

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From: Paul Keinanen on 10 Apr 2010 01:01
On Fri, 09 Apr 2010 20:21:08 -0500, "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?

Sounds quite desperate trying to multiplex the UART.

Are the devices addressable ? If so, an open collector (wired-OR) bus
with 5 V tolerant devices should do the trick.

Could an external dual-UART be used (communicating with the controller
e.g. using I2C) ?

If you end up into a dead end (cost, availability), you may have to
step back a few levels and look at the broader picture.

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