Operation Speed; Instructions To Prevent From Using; Interrupts; How To Access - Renesas M16C/60 Series Hardware Manual

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M16C/6N5 Group

1.14.8 Operation speed

Before entering CPU rewrite mode (EW0 or EW1 mode), select 10 MHz or less for BCLK using the
CM06 bit of the CM0 register and the CM17 to CM16 bits of the CM1 register. Also, set the PM17 bit
of the PM1 register to "1" (with wait state).

1.14.9 Instructions to prevent from using

The following instructions cannot be used in EW0 mode because the flash memory's internal data is
referenced: UND instruction, INTO instruction, JMPS instruction, JSRS instruction, and BRK instruction

1.14.10 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.
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• The NMI and watchdog timer interrupts can be used because the FMR0 register and FMR1 register
are initialized when one of those interrupts occurs. The jump addresses for those interrupt service
routines should be set in the fixed vector table.
Because the rewrite operation is halted when a NMI or watchdog timer interrupt occurs, the rewrite
program must be executed again after exiting the interrupt service routine.
• The address match interrupt cannot be used because the flash memory's internal data is
referenced.
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.
• Avoid using watchdog timer interrupts.
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• The NMI interrupt can be used because the FMR0 register and FMR1 register are initialized when
this interrupt occurs. The jump address for the interrupt service routine should be set in the fixed
vector table.
Because the rewrite operation is halted when a NMI interrupt occurs, the rewrite program must be
executed again after exiting the interrupt service routine.

1.14.11 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 or no DMA transfers will occur before writing "1" after writing "0". Also only
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when NMI pin is "H" level.

1.14.12 Writing in user ROM area

EW0 Mode
• If the power supply voltage drops while rewriting 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. In this case, standard
serial I/O, parallel I/O or CAN I/O mode should be used.
EW1 Mode
• Avoid rewriting any block in which the rewrite control program is stored.

1.14.13 DMA transfer

In EW1 mode, make sure that no DMA transfers will occur while the FMR00 bit of the FMR0 register
= 0 (during the auto program or auto erase period).
Rev.1.00 2003.05.30 page 24
1.14 Precautions for Flash Memory Version
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