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Author Topic: two devices with one UART?  (Read 2857 times)

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Offline AdminTopic starter

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two devices with one UART?
« on: July 23, 2007, 06:26:48 PM »
I want to control both my CMUcam and have a bluetooth connection simultaneously with my ATmega168. Since they both require UART, is this possible?

My guess is that the CMUcam will ignore incorrect commands, and on the bluetooth side I can ignore any data that is CMUcam commands. But not really sure . . .

Or am I being noob like?

Offline hgordon

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Re: two devices with one UART?
« Reply #1 on: July 23, 2007, 08:56:45 PM »
I know the feeling of not having enough serial ports, but it's unlikely that the attached devices would handle the confusion, not to mention issues of different devices pulling the signal lines in opposite directions at the same time.  The only thing you might consider is to add a set of digital switches that route the UART lines between devices under software control.
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Offline AdminTopic starter

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Re: two devices with one UART?
« Reply #2 on: July 24, 2007, 05:44:00 AM »
Quote
The only thing you might consider is to add a set of digital switches that route the UART lines between devices under software control.
Good idea!

Hmmm the best way I can think of doing this is with 4 mosfets (one for each tx and rx line), an inverter, and one digital I/O line. Is there a better way to do this? I feel as if there might be an IC out there already for this . . .

Offline Hal9000

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Re: two devices with one UART?
« Reply #3 on: July 24, 2007, 06:13:30 AM »
I've been doing DSP, but on the maths and not the practicalities!

Aren't you looking for a multiplexer or sorts?
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Offline JonHylands

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Re: two devices with one UART?
« Reply #4 on: July 24, 2007, 06:22:24 AM »
Admin,

Check out the ATmega162 - its a DIP 40, but its got two hardware UARTs.

- Jon

Offline dunk

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Re: two devices with one UART?
« Reply #5 on: July 24, 2007, 06:36:27 AM »
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Check out the ATmega162 - its a DIP 40, but its got two hardware UARTs.
yup. there's quite a few AVRs out there with multiple UARTs.

alternatively you could use one hardware UART and bit bang a 2nd.

dunk.

Offline hgordon

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Re: two devices with one UART?
« Reply #6 on: July 24, 2007, 09:28:03 AM »
alternatively you could use one hardware UART and bit bang a 2nd.
dunk.
Bit banging is a good idea - leave the bluetooth on the UART, since it will be receiving asynchronous requests from the host, while the CMUcam is always under processor control, so you won't lose any data when not watching that software port.
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