M38K09RFS datasheet(269/328 Pages) RENESAS

269 / 328 page

3.2 Notes on use

Rev.2.00

Oct 05, 2006

page 28 of 89

38K0 Group

REJ09B0337-0200

APPENDIX

3.2.11 Notes on stand-by function

(1)

Notes on using stop mode

sRegister setting

Since values of the prescaler 12 and Timer 1 are automatically reloaded when returning from the

stop mode, set them again, respectively. (When the oscillation stabilizing time set after STP

instruction released bit is “0”)

sClock restoration

When the main clock side is set as a system clock, the oscillation stabilizing time for approximately

8,000 cycles of the XIN input is reserved at restoration from the stop mode.

(2)

Notes on stand-by function

In stand-by state*1 for low-power dissipation, do not make input levels of an input port and an I/O

port “undefined”.

Pull-up (connect the port to VCC) these ports through a resistor.

When determining a resistance value, note the following points:

• External circuit

• Variation of output levels during the ordinary operation

When using built-in pull-up resistor, note on varied current values.

• When setting as an input port: Fix its input level

• When setting as an output port: Prevent current from flowing out to external

q Reason

The potential which is input to the input buffer in a microcomputer is unstable in the state that input

levels of an input port and an I/O port are “undefined”. This may cause power source current.

*1 stand-by state : the stop mode by executing the STP instruction

the wait mode by executing the WIT instruction

3.2.12 Notes on CPU rewrite mode

(1)

Operation speed

During CPU rewrite mode, set the internal clock

φ 1.5 MHz or less using the system clock division

ratio selection bits (bits 6 and 7 of address 003B16).

(2)

Instructions inhibited against use

The instructions which refer to the internal data of the flash memory cannot be used during the CPU

rewrite mode .

(3)

Interrupts inhibited against use

The interrupts cannot be used during the CPU rewrite mode because they refer to the internal data

of the flash memory.

(4)

Watchdog timer

In case of the watchdog timer has been running already, the internal reset generated by watchdog

timer underflow does not happen, because of watchdog timer is always clearing during program or

erase operation.

(5)

Reset

Reset is always valid. In case of CNVSS = “H” when reset is released, boot mode is active. So the

program starts from the address contained in address FFFC16 and FFFD16 in boot ROM area.

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