Datasheet

270
42023E–SAM–07/2013
ATSAM4L8/L4/L2
14.5.8 Page Buffer Operations
The flash memory has a write and erase granularity of one page; data is written and erased in
chunks of one page. When programming a page, the user must first write the new data into the
Page Buffer. The contents of the entire Page Buffer is copied into the desired page in flash
memory when the user issues the Write Page command, Refer to Section 14.6.1 on page 275.
In order to program data into flash page Y, write the desired data to locations Y0 to Y31 in the
regular flash memory map. Writing to an address A in the flash memory map will not update the
flash memory, but will instead update location A%32 in the page buffer. The PAGEN field in the
Flash Command (FCMD) register will at the same time be updated with the value A/32.
Figure 14-4. Mapping from Page Buffer to Flash
Internally, the flash memory stores data in 64-bit doublewords. Therefore, the native data size of
the Page Buffer is also a 64-bit doubleword. All locations shown in Figure 14-4 are therefore
doubleword locations. Since the HSB bus only has a 32-bit data width, two 32-bit HSB transfers
must be performed to write a 64-bit doubleword into the Page Buffer. The FLASHCALW has
logic to combine two 32-bit HSB transfers into a 64-bit data before writing this 64-bit data into the
Page Buffer. This logic requires the word with the low address to be written to the HSB bus
before the word with the high address. To exemplify, to write a 64-bit value to doubleword X0
residing in page X, first write a 32-bit word to the byte address pointing to address X0, thereafter
write a word to the byte address pointing to address (X0+4).
The page buffer is word-addressable and should only be written with aligned word transfers,
never with byte or halfword transfers. The page buffer cannot be read.
Z3 Z2 Z1 Z0
Z7 Z6 Z5 Z4
Z11 Z10 Z9 Z8
Z15 Z14 Z13 Z12
Z19 Z18 Z17 Z16
Z23 Z22 Z21 Z20
Z27 Z26 Z25 Z24
Z31 Z30 Z29 Z28
Y3 Y2 Y1 Y0
Y7 Y6 Y5 Y4
Y11 Y10 Y9 Y8
Y15 Y14 Y13 Y12
Y19 Y18 Y17 Y16
Y23 Y22 Y21 Y20
Y27 Y26 Y25 Y24
Y31 Y30 Y29 Y28
X3 X2 X1 X0
X7 X6 X5 X4
X11 X10 X9 X8
X15 X14 X13 X12
X19 X18 X17 X16
X23 X22 X21 X20
X27 X26 X25 X24
X31 X30 X29 X28
3 2 1 0
7 6 5 4
11 10 9 8
15 14 13 12
19 18 17 16
23 22 21 20
27 26 25 24
31 30 29 28
Page X
Page Y
Page Z
Page Buffer
64-bit data
Flash
All locations are doubleword locations