Voltage levels on 90S/Mega8515

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lemiceterrieux
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Posted by lemiceterrieux: Mon. Jun 6, 2022 - 05:55 AM
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Hello ... Does anybody know if the inputs (with deactivated pullups ! ) are compatible with the output levels of a 3.3 V device (powered through an appropriate voltage regulator), or if I should insert some HCT gates to adapt ? Thanks for any answer ...

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AVR Microcontrollers, megaAVR and tinyAVR, solved
Last Edited: Mon. Jun 6, 2022 - 07:31 AM
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Bronze Markjs
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Posted by js: Mon. Jun 6, 2022 - 06:13 AM
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The input should work at 3.3V (over half way) however things are turned on part ways so current drain may increase.

 

The datasheet shows 0.6 of VCC as a valid high input or 3V.

John Samperi

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https://www.ampertronics.com.au

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lemiceterrieux
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Posted by lemiceterrieux: Mon. Jun 6, 2022 - 07:30 AM
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Thanks for the answer ... 0.6 * 5 V = 3 V, I think this a little bit near to the limit ... So I will add some HCT gates, powered with 5 V, or a "level converter".

Last Edited: Mon. Jun 6, 2022 - 07:31 AM
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Bronze Marktheusch
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Posted by theusch: Mon. Jun 6, 2022 - 11:02 AM
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Doesn't all this depend on the Vcc level of your AVR device?

 

What does your datasheet say about input levels?  Are there differences in the datasheet between AT90S8515 and ATmega8515?  [I seem to recall some devices with 0.7V

 

Where did you get a quantity of AT90S devices in 2022?

 

To js:  How does an AVR input turn on part way?  Aren't there Schmitt triggers on all generations?  Isn't the CMOS-latchup situation at 1/2V? 

 

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

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Bronze Marktheusch
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Posted by theusch: Mon. Jun 6, 2022 - 11:15 AM
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https://www.avrfreaks.net/forum/...

ka7ehk wrote:
There is a "stickie" in the Electronics forum about interfacing between various voltage levels. Jim

 

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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