D12320VF25V Datasheet, PDF (658/1146 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 17 ROM
FWE application/disconnection (see figures 17.30 to 17.32): FWE application should be carried
out when MCU operation is in a stable condition. If MCU operation is not stable, fix the FWE pin
low and set the protection state.
The following points must be observed concerning FWE application and disconnection to prevent
unintentional programming or erasing of flash memory:
• Apply FWE when the V_CC voltage has stabilized within its rated voltage range.
Apply FWE when oscillation has stabilized (after the elapse of the oscillation stabilization
time).
• In boot mode, apply and disconnect FWE during a reset.
• In user program mode, FWE can be switched between high and low level regardless of the
reset state. FWE input can also be switched during execution of a program in flash memory.
• Do not apply FWE if program runaway has occurred.
• Disconnect FWE only when the SWE, ESU, PSU, EV, PV, P, and E bits in FLMCR1 are
cleared.
Make sure that the SWE, ESU, PSU, EV, PV, P, and E bits are not set by mistake when
applying or disconnecting FWE.
Do not apply a constant high level to the FWE pin: Apply a high level to the FWE pin only
when programming or erasing flash memory. A system configuration in which a high level is
constantly applied to the FWE pin should be avoided. Also, while a high level is applied to the
FWE pin, the watchdog timer should be activated to prevent overprogramming or overerasing due
to program runaway, etc.
Use the recommended algorithm when programming and erasing flash memory: The
recommended algorithm enables programming and erasing to be carried out without subjecting the
device to voltage stress or sacrificing program data reliability. When setting the P or E bit in
FLMCR1, the watchdog timer should be set beforehand as a precaution against program runaway,
etc.
Do not set or clear the SWE bit during execution of a program in flash memory: Wait for at
least 100 μs after clearing the SWE bit before executing a program or reading data in flash
memory. When the SWE bit is set, data in flash memory can be rewritten, but when SWE = 1,
flash memory can only be read in program-verify or erase-verify mode. Access flash memory only
for verify operations (verification during programming/erasing). Also, do not clear the SWE bit
during programming, erasing, or verifying.
Similarly, when using the RAM emulation function while a high level is being input to the FWE
pin, the SWE bit must be cleared before executing a program or reading data in flash memory.
Rev.7.00 Feb. 14, 2007 page 624 of 1108
REJ09B0089-0700