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PostPosted: Mon Jan 23, 2017 4:33 pm 
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Location: NE Indiana, USA (NTSC)
That would be feasible. Some time ago, tpw_rules was working on a microcontroller project to adapt a PS/2 mouse and keyboard for use with an NES until real life intervened.


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PostPosted: Thu Feb 09, 2017 7:44 am 
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Joined: Tue Jun 24, 2008 8:38 pm
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Location: Fukuoka, Japan
@lidnariq

I have been working a good part of the week with the Raspberry PI and with all the things I had to search to figure out how sensors work (no docs comes with them) and issues with 3v/5v parts I now understand your comment about the Raspberry running at 3v. It feels good to have figured it by myself even though it may seems obvious for people in the know.

At first I was concerned to connect a 1602 LCD I2C screen since the VCC was 5v and the pins on the PI are 3v to the point that I learned how to use a level shifter (didn't know what to use it for before) until I figured out that I2C master/slave, as long master is 3V and the slave doesn't set high on that pin, there is no issue (if the information I found is accurate).

But why the need for 3v, 5v, I'm not sure yet. Is there an historical reason for that? I guess I can figure out by googling but still curious to learn more.


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PostPosted: Thu Feb 09, 2017 11:14 am 
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Joined: Sun Apr 13, 2008 11:12 am
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Location: Seattle
Lower voltage parts can be dramatically more power efficient.

Power consumption for a clocked CMOS part is approximately CV²f, where C is the equivalent bulk capacitance of the whole device, f is its operating frequency, and V is the operating voltage. So using the same part at 3.3V instead of 5V uses only 44% of the power (assuming it can operate at both voltages).

In fact, the majority of modern electronics actually operate at even lower voltages, operating near the lower bound of what silicon-based MOSFETs can do, somewher in the range of 1.2 to 1.8V. The Raspberry Pi is one of these; its I/O voltage is 3.3V but its core voltage is approximately 1.2V.


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PostPosted: Thu Feb 09, 2017 11:55 am 
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Location: NE Indiana, USA (NTSC)
Is there a good reason, other than lack of demand, for there not being a wider variety of ICs (memory, larger CPLDs, and FPGAs) that run 1.2 V internal and 5.0 V external?


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PostPosted: Thu Feb 09, 2017 12:05 pm 
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Location: Seattle
It's mostly lack of demand.

It's also a little harder to design voltage translation to switch to a slightly higher voltage—e.g. the MOSFETs need thicker gates (and thus an extra round in the fab to apply an extra thick layer of quartz in the MOS sandwich) so that the higher externally applied voltages don't exceed whatever the desired safety margin is relative to the breakdown voltage of the quartz dielectric—but I believe this is a small effect in comparison.


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