TC1784
Program Memory Unit (PMU)
User´s Manual
5-15
V1.1, 2011-05
PMU, V1.47
times before refreshing the 64K sector. In total, also for each logical sector the max.
number of erase cycles is 1000. Erase of the 64K physical sector can be performed with
one 64K erase operation or with four 16K erase operations.
Data Flash Sectors
The 128 Kbyte Data Flash is divided into two erasable (physical) sectors of equal size.
The two sectors are identical to the two Flash banks, which are defined to support
concurrent operations. Only in case of read protection, full write protection of DFlash is
supported (can be disabled), but it is not possible to select sector write protection only
for DFlash sectors.
5.6.2.2
Data Flash and EEPROM Emulation
The Data Flash consists of two independent Flash banks (contrary to the Program
Flash). A Data Flash bank also represents a sector, which can be erased only completely
as a unit, and can be programmed page by page. The structure with two independent
Data Flash banks is used to allow simultaneous read or program operations on one bank
while erasing the other bank in the background.
The general structure of the Data Flash is selected to support the emulation of an
EEPROM. In this context, the main difference between a Flash memory and an
EEPROM is the endurance, combined with a shorter retention. For EEPROM, an
endurance of e.g. 120 000 write/erase cycles is required, what is not supported with the
standard Flash memory.
For EEPROM emulation and thus for increasing the endurance, the Data Flash is used
like a circular buffer-memory: The newest data updates are programmed always above
the last programmed page. When the top of sector is reached, all actual data
(representing the actual EEPROM region) are copied to the bottom area of the next
sector and the last sector is then erased. This round robin procedure, using multi-fold
replications of the emulated EEPROM size (called EEPROM regions), significantly
increases the endurance. Thus, the endurance can be selected by changing the size of
emulated EEPROM.
Example 1
The DFLASH is logically divided into four regions (i.e. two per bank) that operate as a
circular buffer memory. At a time, one of the four regions is always regarded as active
EEPROM region. The active EEPROM region is simply identified by the used region with
the highest address within the active DFLASH bank.
The active EEPROM region is held as a EEPROM mirror in an on-chip RAM area. After
a reset operation, the active EEPROM region is copied into the RAM. When the
EEPROM data must be updated, the next consecutive region within the DFLASH circular
Summary of Contents for TC1784
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