M16C26A Datasheet, PDF (262/352 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/Tiny SERIES

M16C/26A Group (M16C/26A, M16C/26B, M16C/26T)
17. Flash Memory Version
17.6 Precautions in CPU Rewrite Mode
Described below are the precautions to be observed when rewriting the flash memory in CPU rewrite mode.
17.6.1 Operation Speed
When CPU clock source is the main clock, before entering CPU rewrite mode (EW0 or EW1 mode),
select 10 MHz or below for CPU clock using the CM06 bit in the CM0 register and the CM17 to CM16
bits in the CM1 register. Also, when selecting f3(ROC) of a on-chip oscillator as a CPU clock source,
before entering CPU rewrite mode (EW0 or EW1 mode), the ROCR3 to ROCR2 bits in the ROCR
register set the CPU clock division rate to “divide-by-4” or “divide-by-8”.
On both cases, set the PM17 bit in the PM1 register to “1” (with wait state).
17.6.2 Prohibited Instructions
The following instructions cannot be used in EW0 mode because the CPU tries to read data in the
flash memory: UND instruction, INTO instruction, JMPS instruction, JSRS instruction, and BRK in-
struction
17.6.3 Interrupts
EW0 Mode
• To use interrupts having vectors in a relocatable vector table, the vectors must be relocated to the
RAM area.
_______
• The NMI and watchdog timer interrupts can be used since the FMR0 and FMR1 registers are
forcibly reset when either interrupt is generated. However, the jump addresses for each interrupt
service routines to the fixed vector table are set and interrupt programs are required. Flash
memory rewrite operation is halted when the NMI or watchdog timer interrupt is generated. Set the
FMR01 bit to “1” and execute the rewrite and erase program again after exiting the interrupt rou-
tine.
• The address match interrupt can not be used since the CPU tries to read data in the flash memory.
EW1 Mode
• Do not acknowledge any interrupts with vectors in the relocatable vector table or the address
match interrupt during the auto-program or erase-suspend function.
17.6.4 How to Access
To set the FMR01, FMR02, FMR11 or FMR16 bit to “1”, write “1” after first setting the bit 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 P85/
_______ _____
NMI/SD pin.
17.6.5 Writing in the User ROM Space
17.6.5.1 EW0 Mode
• 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.
17.6.5.2 EW1 Mode
• Do not rewrite the block where the rewrite control program is stored.
Rev. 2.00 Feb.15, 2007 ^{page 245} of 329
REJ09B0202-0200