NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.

RC Timing Notes

General Formula:

 t_a®b = -RC · ln ( (V-b) / (V-a) )

• V = Forcing voltage
• B = Voltage at the end of the timing interval
• A = Voltage at the beginning of the timing interval

Often Used Calculations:

 10% ® 90% =  2.2 RC

 20% ® 80% =  1.4 RC

  0% ® 40% = 0.51 RC (to 2V)

0.8V ® 2V  = 0.34 RC (VCC=5V)

Excel Timing Calculator:

rc_calculator.xls

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Last Revised: November 27, 2003
Digital Engineering Institute
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