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Old 11-14-2011, 06:40 PM
Atomic10 Atomic10 is offline
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Default CMOS and LVTTL Voltage Levels

For 1.8V, 2.5V, 2.7V, and 3.3V, what are the acceptable low and high voltage ranges for CMOS and LVTTL?

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Old 11-14-2011, 06:47 PM
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This should help you:
http://www.interfacebus.com/voltage_LV_threshold.html

Low Voltage Logic Threshold Levels

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Old 11-14-2011, 07:19 PM
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What do I do for different voltages, including 1.8V, 2.5V, 2.7V, and 3.3V? The attached chart is only for 5V.
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Old 11-14-2011, 08:06 PM
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As you move to the right, you'll see the top of the chart is 3.3V. 2.5V Logic, such as Microchip's published minimum operating voltage on some microcontrollers, is a difficult voltage to interface with externally, as 2.5v is considered High or indeterminate value on 3.3V logic, and low or indeterminate on 5V CMOS.

The far right represents most "low voltage" implementations, as percentages of Supply voltage, which can be applied from 2V to 3.5V

Today's x86 and x64 CPUs run at 1V-1.25V Vdd, and their logic isn't as standard as the chart above, internal to the die, except for the slower external signals, the levels only need to meet the proprietary internal standards of the CPU.
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