8XC196MC, MD, MH USER’S MANUAL

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 C1.

TDIS × I

C1 = -------------------

Vt

where:

C1

is the capacitor value, in farads

TDIS

is the worst-case discharge time, in seconds

I

is the discharge current, in amperes

Vt

is the threshold voltage

NOTE

If powerdown is re-entered and exited before C1 charges to VCC, it will take less time for the voltage to ramp down to the threshold. Therefore, the device will take less time to exit powerdown.

For example, assume that the oscillator needs at least 12.5 ms to discharge (TDIS

= 12.5 ms), Vt

is 2.5 V, and the discharge current is 200 μA. The minimum C1 capacitor size is 1

μF.

C =

( 0.0125) ( 0.0002)

 

-------------------------------------------------- = 1 μ F

 

1

2.5

 

 

 

When using an external oscillator, the value of C1 can be very small, allowing rapid recovery from powerdown. For example, a 100 pF capacitor discharges in 1.25 μs.

C1

× Vt

 

( 1.0 × 1010)

( 2.5)

1.25 μs

TDIS = ---------

I---------

=

-----------------0.0002---------------------

------------=

 

 

 

 

14.5 ONCE MODE

On-circuit emulation (ONCE) mode isolates the device from other components in the system to allow printed-circuit-board testing or debugging with a clip-on emulator. During ONCE mode, all pins except XTAL1, XTAL2, VSS, and, VCC are weakly pulled high or low. During ONCE mode, RESET# must be held high or the device will exit ONCE mode and enter the reset state.

14-10

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Intel 8XC196MC, 8XC196MD, 8XC196MH manual Once Mode