AT89LP428 datasheet(13/149 Pages) ATMEL

13 / 149 page

3654A–MICRO–8/09

AT89LP428/828

Figure 3-4.

FDATA Byte Write

Figure 3-5.

FDATA Page Write

The auto-erase bit AERS (MEMCON.6) can be set to one to perform a page erase automatically

at the beginning of any write sequence. The page erase will erase the entire page and then the

bytes in the temporary buffer will be written to the selected page.

Frequently just a few bytes within a page must be updated while maintaining the state of the

other bytes. There are two options for handling this situation that allow the Flash data memory to

emulate a traditional EEPROM memory. The simplest method is to copy the entire page into a

buffer allocated in RAM, modify the desired byte locations in the RAM buffer, and then load and

write back the page to the Flash memory. This option requires that at least one page size of

RAM is available as a temporary buffer. The second option is to load the unmodified bytes of the

page directly into the Flash memory’s temporary load buffer before loading the updated values

of the modified bytes. For example, if just one byte needs modification, the user must first read

and load the unaffected bytes of into the page buffer. Then the modified byte value is stored to

the page buffer before starting the auto-erase sequence. This method reduces the amount of

RAM required; however, more software overhead is needed because the read-and-load-back

routine must skip those bytes in the page that need to be updated in order to prevent those loca-

tions in the buffer from being loaded with the previous data, as this will block the new data from

being loaded correctly.

A write sequence will not occur if the Brown-out Detector (BOD) is active, even if the BOD reset

has been disabled. In cases where the BOD reset is disabled, the user should check the BOD

status by reading the WRTINH bit in MEMCON. If a write currently in progress is interrupted by

the BOD due to a low voltage condition, the ABORT flag will be set. FDATA can always be read

regardless of the BOD state.

For more details on using the Flash Data Memory, see the application note titled “AT89LP Flash

Data Memory”. FDATA may also be programmed by an external device programmer (see “Pro-

gramming the Flash Memory” on page 115).

MWEN

DMEN

LDPG

IDLE

MOVX

MWEN

DMEN

LDPG

IDLE

MOVX

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