AT89LP51 datasheet(17/113 Pages) ATMEL

17 / 113 page

3709C–MICRO–5/11

AT89LP51/52 - Preliminary

The LDPG bit (MEMCON.5) allows multiple data bytes to be loaded to the temporary page buf-

fer. While LDPG = 1, MOVX @DPTR,A instructions will load data to the page buffer, but will not

start a write sequence. Note that a previously loaded byte must not be reloaded prior to the write

sequence. To write the half page into the memory, LDPG must first be cleared and then a

MOVX @DPTR,A with the final data byte is issued. The address of the final MOVX determines

which half page will be written. If a MOVX @DPTR,A instruction is issued while LDPG = 0 with-

out loading any previous bytes, only a single byte will be written. The page buffer is reset after

each write operation. Figures 3-8 and Figure 3-9 on page 17 show the difference between byte

writes and page writes.

Figure 3-8.

FDATA Byte Write

Figure 3-9.

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, i.e. both the

low and high half pages. However, the write operation paired with the auto-erase can only pro-

gram one of the half pages. A second write cycle without auto-erase is required to update the

other half 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 first the low half page (with auto-erase) and then the high half page to the Flash mem-

ory. This option requires that at least one page size of RAM is available as a temporary buffer.

The second option is to store only one half page in RAM. The unmodified bytes of the other page

are loaded directly into the Flash memory’s temporary load buffer before loading the updated

values of the modified bytes. For example, if just the low half page needs modification, the user

must first store the high half page to RAM, followed by reading and loading the unaffected bytes

of the low half page into the page buffer. Then the modified bytes of the low half page are stored

MWEN

DMEN

LDPG

IDLE

MOVX

MWEN

DMEN

LDPG

IDLE

MOVX

AT89LP51 Datasheet(PDF) 17 Page - ATMEL Corporation