38D2 datasheet(91/136 Pages) RENESAS

91 / 136 page

Rev.3.02

Apr 10, 2008

Page 91 of 131

REJ03B0177-0302

38D2 Group

NOTES ON FLASH MEMORY VERSION

CPU Rewrite Mode

(1) Operation speed

During CPU rewrite mode, set the system clock

φ 4.0 MHz or

less using the main 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.

CNVSS Pin

The CNVSS pin determines the flash memory mode.

Connect the CNVSS/VPP pin the shortest possible to the GND

pattern which is supplied to the VSS pin of the microcomputer.

In addition connecting an approximately 5 k

Ω. resistor in series

to the GND could improve noise immunity. In this case as well as

the above mention, connect the pin the shortest possible to the

GND pattern which is supplied to the VSS pin of the

microcomputer.

Note. When the boot mode or the standard serial I/O mode is used, a

switch of the input level to the CNVSS pin is required.

Fig 89. Wiring for the CNVSS

NOTES ON DIFFERENCES BETWEEN QzROM

VERSION AND FLASH MEMORY VERSION

The QzROM version and flash memory versions differ in their

manufacturing processes, built-in ROM, and layout patterns.

Because of these differences, characteristic values, operation

margins, noise immunity, and noise radiation and oscillation

circuit constants may vary within the specified range of electrical

characteristics.

When switching to the QzROM version, implement system

evaluations equivalent to those performed in the flash memory

version.

Confirm page 11 about the differences of functions.

The shortest

CNVSS

VSS

Approx. 5k

The shortest

(1)

Note 1: It shows the microcomputer’s pin.

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