I2C devices with same address on one avr chip

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nick-123
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Posted by nick-123: Tue. Jul 15, 2008 - 04:58 PM
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I've noticed that a ds3232 rtc chip had a time difference of 0.06 ppm after 16 months (2.5s / 16 months). This seems ridiculous low (datasheet: 2ppm), so I would like to check this with several chips simultaneously.

I have not yet any good idea's on how to accomplish this. The I2C address is the same. Is there a simple method to multiplex I2C?

Nick

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AVR Microcontrollers, megaAVR and tinyAVR
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glitch
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Posted by glitch: Tue. Jul 15, 2008 - 05:07 PM
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you will need separate busses. You devices cannot share the same address on the bus.

You may be able to find i2c transceivers which can be enabled/disabled via some control line. (LTC4300 may work)

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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Bronze Marktheusch
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Posted by theusch: Tue. Jul 15, 2008 - 05:12 PM
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Hmmm--apparently Dallas/Maxim didn't think of the case where more than one "extremely accurate" RTC would be needed on the same I2C bus. ;)

Burn an Xmega for your long-term test, with 4 I2C ports?

With "normal" RTCs I tested a batch for a short time, and the results were a bell curve. Yours could just be at the nominal. Also, the 2ppm is over the entire temperature range. Performance is likely to be better at constant temperature. It >>is<< rated from -2ppm min to +2ppm max, so you are really in the "TYP" range.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Bronze Markjs
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Posted by js: Wed. Jul 16, 2008 - 12:29 AM
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Quote:
This seems ridiculous low
But that's what you (and me) are paying for, presumably. It has a built in TCXO.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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nick-123
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Posted by nick-123: Wed. Jul 16, 2008 - 12:38 AM
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Yeah, it's a cool chip. Great RTC. Comes with an integrated temperature sensor.

Oh, I think I'll go with some ti chips (PCA9548A - 8-Channel I2C Switch With Reset or a PCA9545A - 4-Channel I2C And SMBus Multiplexer With Interrupt Logic And Reset Functions) to solve my little problem.

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rberger
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Posted by rberger: Wed. Jul 16, 2008 - 04:14 PM
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Quote:
I have not yet any good idea's on how to accomplish this. The I2C address is the same. Is there a simple method to multiplex I2C?

Last time I looked at this was to multiplex 8 I2C devices.

The original project bitbsahed 8 independant ports.
No Way Am I Going To Do That!

I suggest using an 74HC4051 style multiplexor to rout the "Data" to the addressed device, since the clock alone doesnt enlicit a response.
Ron.

 

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nick-123
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Posted by nick-123: Sat. Jul 19, 2008 - 02:42 PM
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Thanks

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