AT89C51RE2 Datasheet, PDF (41/187 Pages) ATMEL Corporation – 8-bit Flash Microcontroller

AT89C51RE2
Loading the Column
Latches
Any number of data from 0 byte to 128 bytes can be loaded in the column latches. The data writ-
ten in the column latches can be written in a none consecutive order. The DPTR allows to select
the address of the byte to load in the column latches.
The page address to be written (target page in FM0) is given by the last address loaded in the
column latches and when this page belongs to the upper 32K bytes of the logical addressable
MCU space, the target memory bank selection is performed upon the MBO2:0 value during the
last address loaded.
When 0 byte is loaded in the column latches the activation sequence (5xh, Axh in FCON) does
not launch any operations. The FSE bit in FSTA register is set.
When a current flash write operation is on-going (FBUSY is set), it is impossible to load the col-
umns latches before the end of flash programming process (the write operation in the columns
latches is not performed, and the previous columns latches content is not overwritten).
When programming is launched, an automatic erase of the entire memory page is first per-
formed, then programming is effectively done. Thus no page or block erase is needed and only
the loaded data are programmed in the corresponding page. The unloaded data of the target
memory page are programmed at 0xFF value (automatic page erase value).
The following procedure is used to load the column latches and is summarized in Figure 13:
• Disable interrupt and map the column latch space by setting FPS bit.
• Select the target memory bank (for page address larger than 32K)
• Map the column latch
• Reset the column latch
• Load the DPTR with the address to write.
• Load Accumulator register with the data to write.
• Execute the MOVX @DPTR, A instruction, and only this one (no MOVX @Ri, A).
• If needed loop the last three instructions until the page is completely loaded.
• Unmap the column latch if needed (it can be left mapped) and Enable Interrupt
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