Writing The Data - Fujitsu MB90460 Series Hardware Manual

CHAPTER 23 512K / 1024K BIT FLASH MEMORY
23.6.2

Writing the Data

This section explains the procedure of issuing the write command and writing the data
to the flash memory. Figure 23.6-1 shows an example of procedure of writing data to
the flash memory.
■ Writing the Data
The automatic algorithm for writing the data to the flash memory can be performed by continuously
sending the write command, listed in the command sequence table (see "23.4 Method of Starting the
Automatic Algorithm in Flash Memory"), to the target sector in the flash memory. When the data write
operation to the target address in the 4th cycle has been terminated, the automatic algorithm is started for
automatic writing.
■ How to Specify the Address
Only even addresses can be specified as the write address in the write data cycle. If an odd address is
specified, data cannot be correctly written. That is, it is necessary to write the data in units of words to
even addresses.
Data can be written to the flash memory, and any address sequence may be specified, even if data has been
written across the sector boundary. However, only one-word data can be written by executing the write
command once.
■ Notes on Writing the Data
By writing the data, data "0" cannot be returned to data "1". If data "1" is written to data "0", the data
polling algorithm (DQ7) or toggle operation (DQ6) is not terminated and the flash memory element is
determined to be bad. Then, the time limit exceeded flag (DQ5) error may be determined by the excess of
the write defined time, or data "1" may be apparently written but is not actually done. However, if data is
read from the flash memory in the read/reset status, data remains "0". Only the deletion operation enables
data "0" to be changed to data "1".
All commands are ignored while automatic writing is being performed. Note that the data at the address for
writing is not assured if the hardware is reset during automatic writing.
■ Procedure of Writing the Data to the Flash Memory
Figure 23.6-1 shows an example of procedure of writing the data to the flash memory. Using the hardware
sequence flag (see "23.5 Verifying Automatic Algorithm Execution Status"), the status of the automatic
algorithm within the flash memory can be determined. Here, the data polling flag (DQ7) is used for
verifying the end of writing.
The data reading for checking the flag is started from the last-written address. The data polling flag (DQ7)
is changed at the same time when the time limit exceeded flag (DQ5) is changed, so the data polling flag
(DQ7) must be rechecked even if the time limit exceeded flag (DQ5) is "1".
Similarly, the toggle bit flag (DQ6) stops the toggle operation at the same time when the time limit
exceeded flag (DQ5) is changed to "1", so the toggle bit flag (DQ6) must be rechecked.
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