Datasheet
259
32117D–AVR-01/12
AT32UC3C
Figure 15-3. Mapping from Page Buffer to Flash
The page buffer is word-addressable and should only be written with aligned word transfers,
never with byte or halfword transfers. The page buffer can not be read.
The page buffer is also used for writes to the User page.
Page buffer write operations are performed with 4 wait states. Any accesses attempted to the
FLASHC on the HSB bus during these cycles will be automatically stalled.
Writing to the page buffer can only change page buffer bits from one to zero, i.e. writing
0xAAAAAAAA to a page buffer location that has the value 0x00000000 will not change the page
buffer value. The only way to change a bit from zero to one is to erase the entire page buffer with
the Clear Page Buffer command.
The page buffer is not automatically reset after a page write. The programmer should do this
manually by issuing the Clear Page Buffer flash command. This can be done after a page write,
or before the page buffer is loaded with data to be stored to the flash page.
15.4.9 Writing Words to a Page that is not Completely Erased
This can be used for EEPROM emulation, i.e. writes with granularity of one word instead of an
entire page. Only words that are in an completely erased state (0xFFFFFFFF) can be changed.
The procedure is as follows:
35 34 33 32
39 38 37 36
43 42 41 40
47 46 45 44
51 50 49 48
55 54 53 52
59 58 57 56
63 62 61 60
Page Buffer
32-bit data
Flash
All locations are word locations
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
X35 X34 X33 X32
X39 X38 X37 X36
X43 X42 X41 X40
X47 X46 X45 X44
X51 X50 X49 X48
X55 X54 X53 X52
X59 X58 X57 X56
X63 X62 X61 X60
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
Page X
Y35 Y34 Y33 Y32
Y39 Y38 Y37 Y36
Y43 Y42 Y41 Y40
Y47 Y46 Y45 Y44
Y51 Y50 Y49 Y48
Y55 Y54 Y53 Y52
Y59 Y58 Y57 Y56
Y63 Y62 Y61 Y60
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
Page Y