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Read/Reset Command
To return to read mode after the time limit is exceeded, a read/reset command sequence will be issued.
Data is read from flash memory in the read cycle. The flash memory remains in reading state until another
command is entered.
When the power is turned on, flash memory is automatically set to the read/reset state. In this case, data can
be read without a command of the automatic algorithm.
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Program (Write)
In CPU programming mode, data is basically written in halfword units. The write operation is performed
in four cycles of bus operation. The command sequence has two "unlock" cycles, which are followed by a
write setup command and a write data cycle. Writing to the memory starts in the last write cycle.
After an automatic write algorithm command sequence was executed, it becomes unnecessary to control the
flash memory externally. The flash memory itself internally generates write pulses to check the margin of
the cells to which data is written. The data polling function compares bit7 of the original data with bit7 of
the written data, and if these bits are the same, the automatic write operation ends (see "■Hardware
Sequence Flag" in section "17.5 Automatic Algorithm Execution Status"). The automatic write operation
then returns to the read mode and accepts no more write addresses. After that, the flash memory requests
the next valid address. In this manner, the data polling function indicates the memory is in a write
operation.
During a write operation, all commands written to the flash memory are ignored. If a hardware reset starts
during write operation, the data at the address for writing may become invalid. Writing operations can be
performed in any address sequence and outside of sector boundaries. However, write operations cannot
change a data item "0" to "1". If a "0" is overwritten with a "1", either the data polling algorithm
determines that the elements are defective, or it looks as if "1" has been written. In the latter case, however,
the respective data item is read as "0" in reset/read mode. A data item "0" can be changed to "1" only by an
erase operation. Figure 17.4-1 shows a writing sequence with using write command.
Figure 17.4-1 Writing Sequence with Using Write Command
Write command sequence
Data polling of the device
NO
Next address
CHAPTER 17 FLASH MEMORY
Write starts
Last address?
YES
Write ends
417
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