Precautions In Cpu Rewrite Mode; Operation Speed; Prohibited Instructions; Interrupts - Renesas M16C FAMILY series Hardware Manual

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18.6 Precautions in CPU Rewrite Mode

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

18.6.1 Operation Speed

When the CPU clock source is the main clock, set the CPU clock frequency at 10 MHz or less with the
CM06 bit in the CM0 register and the CM17 and CM16 bits in the CM1 register, before entering CPU
rewrite mode (EW mode 0 or EW mode 1). Also, when selecting f
clock source, set the ROCR3 and ROCR2 bits in the ROCR register to the CPU clock division rate at
"divide-by-4" or "divide-by-8", before entering CPU rewrite mode (EW mode 0 or EW mode 1).
In both cases, set the PM17 bit in the PM1 register to "1" (with wait state).

18.6.2 Prohibited Instructions

The following instructions cannot be used in EW mode 0 because the CPU tries to read data in the flash
memory: UND instruction, INTO instruction, JMPS instruction, JSRS instruction, and BRK instruction

18.6.3 Interrupts

EW Mode 0
• To use interrupts having vectors in a relocatable vector table, the vectors must be relocated to the
RAM area.
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• The NMI and watchdog timer interrupts are available since the FMR0 and FMR1 registers are
forcibly reset when either interrupt occurs. However, the interrupt program, which allocates the
jump addresses for each interrupt routine to the fixed vector table, is needed. Flash memory
rewrite operation is aborted when the NMI or watchdog timer interrupt occurs. Set the FMR01 bit
to "1" and execute the rewrite and erase program again after exiting the interrupt routine.
• The address match interrupt can not be used since the CPU tries to read data in the flash memory.
EW Mode 1
• Do not acknowledge any interrupts with vectors in the relocatable vector table or the address
match interrupt during the auto program period or auto erase period with erase-suspend function
disabled.

18.6.4 How to Access

To set the FMR01, FMR02, FMR11 or FMR16 bit to "1", write "1" immediately after setting to "0". Do not
generate an interrupt or a DMA transfer between the instruction to set the bit to "0" and the instruction to
set it to "1". When the NMI function is selected, set the bit while an "H" signal is applied to the P8
pin.

18.6.5 Writing in the User ROM Area

18.6.5.1 EW Mode 0
• If the supply voltage drops while rewriting the block where the rewrite control program is stored,
the flash memory can not be rewritten, because the rewrite control program is not correctly rewrit-
ten. If this error occurs, rewrite the user ROM area in standard serial I/O mode or parallel I/O
mode.
18.6.5.2 EW Mode 1
• Do not rewrite the block where the rewrite control program is stored.
R e . v 2 0 . 0 J a . n 3 , 1 2 0 0 7
R E J 0 9 B 0 0 4 7 0 - 2 0 0
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18. Flash Memory Version
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