M16CSLASH1N datasheet(198/238 Pages) RENESAS

198 / 238 page

Rev.1.00

Oct 20, 2004

page 186 of 222

M16C/1N Group

19. Flash Memory Version

REJ09B0007-0100Z

19.5.3 Precautions on CPU Rewrite Mode

Described below are the precautions to be observed when rewriting the flash memory in CPU rewrite

mode.

(1) Operation speed

Before entering CPU rewrite mode (EW0 or EW1 mode), select 10 MHz or less for BCLK using the

CM0 register's CM06 bit and CM1 register's CM17–6 bits. Also, set the PM1 register's PM17 bit to "1"

(with wait state).

(2) Instructions inhibited against use

In EW0 mode, the following instructions cannot be used because the flash memory's internal data is

referenced: UND instruction, INTO instruction, JMPS instruction, JSRS instruction, and BRK instruc-

tion

(3) Interrupts

EW0 mode

• Any interrupt which has a vector in the variable vector table can be used providing that its vector is

transferred into the RAM area.

• The watchdog timer interrupt can be used because the FMR0 register and FMR1 register are

initialized when one of those interrupts occurs. However, it is necessary that the jump addresses

for those interrupts are set in the fixed vector table, and that interrupt service routines are available

for those interrupts.

Because the rewrite operation is halted when a watchdog timer interrupt occurs, the FMR01 bit

must be set back to "1" again in order to enable erase or programming operation after exiting the

interrupt service routine.

• The address match interrupt cannot be used because the flash memory's internal data is refer-

enced.

EW1 mode

• Make sure that any interrupt which has a vector in the variable vector table or address match

interrupt will not be accepted during the auto program or auto erase period.

(4) How to access

To set the FMR01, FMR02, or FMR11 bit to "1", write "0" and then "1" in succession. This is necessary

to ensure that no interrupts will occur before writing "1" after writing "0".

(5) Writing in the user ROM area

If the power supply voltage drops while rewriting in EW0 mode any block in which the rewrite control

program is stored, a problem may occur that the rewrite control program is not correctly rewritten and,

consequently, the flash memory becomes unable to be rewritten thereafter. It is recommended that

such a block be rewritten using standard serial I/O, CAN I/O or parallel I/O mode.

(6) Writing command and data

Write the command code and data at even addresses.

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