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15.9.3
Erase Mode
Flash memory erasing should be performed block by block following the procedure shown in the
erase/erase-verify flowchart shown in figure 15-15.
For the wait times (t
sswe, tsesu, tse, tce, tcesu, tsev, tsevr, tcev, tcswe) after bits are set or cleared in flash
memory control register 1 (FLMCR1) and the maximum number of erase operations (N), see
section 18.6, Flash Memory Characteristics.
To perform data or program erasure, make a 1-bit setting for the flash memory area to be erased in
erase block register 1 or 2 (EBR1 or EBR2) at least t
sswe s after setting the SWE1 bit to 1 in flash
memory control register 1 (FLMCR1). Next, set up the watchdog timer to prevent overerasing in
the event of program runaway, etc. Set a value greater than (t
sesu + tse + tce + tcesu) s as the WDT
overflow period. After this, preparation for erase mode (erase setup) is carried out by setting the
ESU1 bit in FLMCR1, and after the elapse of t
sesu s or more, the operating mode is switched to
erase mode by setting the E1 bit in FLMCR1. The time during which the E1 bit is set is the flash
memory erase time. Ensure that the erase time does not exceed t
se ms.
Note:
With flash memory erasing, prewriting (setting all data in the memory to be erased to 0) is
not necessary before starting the erase procedure.
15.9.4
Erase-Verify Mode
In erase-verify mode, data is read after memory has been erased to check whether it has been
correctly erased.
In erase-verify mode, data is read after memory has been erased to check whether it has been
correctly erased.
After the elapse of the erase time, erase mode is exited (the E1 bit in FLMCR1 is cleared to 0, then
the ESU1 bit is cleared to 0 at least t
ce s later), the watchdog timer is cleared after the elapse of
t
cesu s or more, and the operating mode is switched to erase-verify mode by setting the EV1 bit in
FLMCR1. Before reading in erase-verify mode, a dummy write of H'FF data should be made to
the addresses to be read. The dummy write should be executed after the elapse of tsev s or more.
When the flash memory is read in this state (verify data is read in 16-bit units), the data at the
latched address is read. Wait at least t
sevr s after the dummy write before performing this read
operation. If the read data has been erased (all 1), execute a dummy write to the next address, and
perform an erase-verify. If the read data has not been erased, set erase mode again and repeat the
erase/erase-verify sequence as before. However, ensure that the erase/erase-verify sequence is not
repeated more than (N) times. When verification is completed, exit erase-verify mode, and wait
for at least t
cev s. If erasure has been completed on all the erase blocks, clear the SWE1 bit in
FLMCR1. If there are any unerased blocks, make a 1-bit setting for the flash memory block to be
erased, and repeat the erase/erase-verify sequence as before.