M38042FEHKP datasheet(92/387 Pages) RENESAS

92 / 387 page

1-74

REJ09B0212-0100Z

Rev.1.00

Jan 14, 2005

3804 Group (Spec.H)

HARDWARE

FUNCTIONAL DESCRIPTION

RESET CIRCUIT

To reset the microcomputer, RESET pin should be held at an “L”

level for 16 cycles or more of XIN. Then the RESET pin is returned

to an “H” level (the power source voltage should be between 2.7 V

to 5.5 V, and the oscillation should be stable), reset is released.

After the reset is completed, the program starts from the address

contained in address FFFD16 (high-order byte) and address

FFFC16 (low-order byte).

Input to the RESET pin in the following procedure.

qWhen power source is stabilized

(1) Input “L” level to RESET pin.

(2) Input “L” level for 16 cycles or more to XIN pin.

(3) Input “H” level to RESET pin.

qAt power-on

(1) Input “L” level to RESET pin.

(2) Increase the power source voltage to 2.7 V.

(3) Wait for td(P-R) until internal power source has stabilized.

(4) Input “L” level for 16 cycles or more to XIN pin.

(5) Input “H” level to RESET pin.

Fig. 71 Reset sequence

Fig. 70 Reset circuit example

RESET

Internal

reset

Data

Address

SYNC

XIN: 10.5 to 18.5 clock cycles

XIN

FFFC

FFFD

ADH,L

ADL

ADH

1: The frequency relation of f(XIN) and f(

φ) is f(XIN)=8 • f(φ).

2: The question marks (?) indicate an undefined state that depends on the previous state.

Reset address from the vector table.

Notes

VCC

RESET

VCC

RESET

Example at VCC = 5V

td(P-R)+XIN 16 cycles or more

2.7 V

0.2VCC or less

VCC

RESET

VCC

RESET

td(P-R)+XIN 16 cycles or more

2.7 V

Power source

voltage detection

circuit

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