MPC821 datasheet(87/242 Pages) NXP

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MPC8XXFADS Design Specification—Rev 0.1

PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE

"* Reset MPC8XX. (Connected to MPC8XX hard and reset inputs) Asynchronous.

"******************************************************************************

equations

!PdaHardReset~ = H;

PdaHardReset~.oe = PdaHardResetEn;

"open-drain

PdaHardResetEn = ADS_IS_SELECTED &

(AdsHardReset==ADS_HARD_RESET_ACTIVE);

!PdaSoftReset~ = H;

PdaSoftReset~.oe = PdaSoftResetEn;

"needs to be open-drain

PdaSoftResetEn = ADS_IS_SELECTED &

(AdsSoftReset==ADS_SOFT_RESET_ACTIVE );

"******************************************************************************

"* Clock generator.

"* All i/f logic works on IClk, which is driven externally by the output

"* of DbgClk divider.

"* The debug clock divider is a 3 bit free-running counter, outputs of which

"* control a 4:1 mux, output of which drives IClk (externally).

"* Since mux control may change on the fly, a protection logic by means of

"* 2 bit register is provided, so that mux control is allowed to change

"* only when all divider outputs are high which assures a falling edge prior

"* to a rising edge.

"* Clk2 is infact the source for DSCK and is available outside for debug

"* purpose.

"******************************************************************************

equations

DbgClkDiv.clk = DbgClk;

DbgClkDiv := DbgClkDiv.fb + 1; " free running counter.

"******************************************************************************

"* Clock Safe Transition Register. (CSTR)

"* The goal of this register is to provide safe clock transitions, i.e., that

"* a trasition will not cause races over the clockout. E.g., in a transition

"* between divide by 1 and divide by any bigger order, a possible race may

"* occur since the divided outputs are delayed with respect to DbgClk.

"* Therefore, a safe transition may be performed only when all clocks are LOW.

"******************************************************************************

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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