Intel 80C196NU User Manual

12-11

When selecting the capacitor, determine the worst-case discharge time needed for the oscillator
to stabilize, then use this formula to calculate an appropriate value for C

1

.

where:

C

1

is the capacitor value, in farads

T

DIS

is the worst-case discharge time, in seconds

I

is the discharge current, in amperes

V

t

is the threshold voltage

If powerdown is re-entered and exited before C

1

 charges to V

CC

, it will take 

less time for the voltage to ramp down to the threshold. Therefore, the device 
will take less time to exit powerdown. 

1

2

3

4

5

200 

µ

A C1 Discharge   

Code Execution

Resumes

EXTINT

x

Time, ms

2

4

6

8

10

12

14

16

18

20

22

RPD, Volts 

A2385-02

VCC  =  5 V

VCC  =  3 V

.8 V

1.2 V

3 V

5 V

C

1

T

DIS

I

×

V

t

--------------------

=