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CHAPTER 17 FLASH MEMORY
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Chip Erase
The chip erase ("erase all sectors simultaneously") is executed in six access cycles. First, two "unlock"
cycles are executed, and then a "setup" command is written. Two more "unlock" cycles are executed to
enter the chip erase command.
During the chip erase, the user does not have to write to flash memory before the erase operation. When
the automatic erase algorithm is executed, flash memory checks cell states by writing a pattern of zeros
before automatically erasing the contents of all cells (preprogram). In this operation, flash memory does
not have to be controlled externally.
The automatic erase operation starts with the write operation of the command sequence and ends when bit7
is set to "1", where flash memory returns to the read mode. The chip erase time can be expressed as
follows: time for sector erase x number of all sectors + time for writing to the chip (preprogram).
Figure 17.4-2 shows chip erasing sequence with using chip erase command.
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Sector Erase
The sector erase is executed in six access cycles. First, two "unlock" cycles are executed, and then a
"setup" command is written. After two more "unlock" cycles, the sector erase command is entered in the
sixth cycle for starting the sector erase operation. The next sector erase command can be accepted within a
time-out period of 50 µs after the last sector erase command was written.
Multiple sector erase commands can be accepted concurrently during the six bus cycles of the writing
operation as mentioned above. This command sequence is executed by writing sector erase commands
(30
) consecutively into the addresses for sectors whose contents are to be erased simultaneously. The
H
sector erase operation itself starts from the end of the time-out period of 50 µs after the last sector erase
command is written. Therefore, when the contents of multiple sectors are erased simultaneously, the
subsequent sector erase commands must be inputted within the 50 µs time-out period to ensure that they are
accepted. If the commands are inputted after the 50 µs time-out period, the commands may not be
accepted. For checking whether the succeeding sector erase command is valid, read bit3 (see "■Hardware
Sequence Flag" in section "17.5 Automatic Algorithm Execution Status").
During the time-out period, any commands other than sector erase and temporary stop erase are reset to
read, and the preceding command sequence is ignored. In the case, the erase operation is completed by
erasing the contents of the sector again. Any combination and number (from 0 to 6) of sector addresses can
be entered in the sector erase buffers. The user does not have to write to flash memory before the sector
erase operation. Flash memory automatically writes to all cells in a sector whose data is automatically
erased (preprogram). When the contents of a sector are erased, the other sectors remain intact. In these
operations, flash memory does not have to be controlled externally.
The automatic sector erase operation starts from the end of the 50 µs time-out period after the last sector
erase command is written. When bit7 is set to "1", the automatic sector erase operation ends and flash
memory returns to the read mode (see "■Hardware Sequence Flag" in section "17.5 Automatic Algorithm
Execution Status"). At this time, other commands are ignored. The data polling function is enabled for any
sector address in which data has been erased. The time required for erasing the data of multiple sectors can
be expressed as follows: time for sector erase + time for sector write (preprogram) × number of erased
sectors.
Figure 17.4-2 shows chip erasing sequence with using chip erase command.
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